Citroen's approach to suspension

[rover3l]

Not quite the same as a Q45a but still pretty sophisticated. This is an article about citroen hydro pneumatic suspension with active roll control.

Hydropneumatic suspensionWHAT CITROËNS ARE ALL ABOUT:PUMPS, PRESSURE, AND GREEN MINERAL OILCitroën's André Lefebvre began to experiment with hydraulics for car suspension in the 1940s, and by 1954 he had developed a hydropneumatic system in which a column of oil compressed a bag of nitrogen gas, which served as a spring.Hydropneumatic suspension was first seen on the rear axle of the big six-sylinder 15/6 H Traction Avant and it was developed for a wider market on the DS19 at 1955. Hydropneumatic suspension has been a major factor in Citroën's supremacy in the art of roadholding and comfort since 1954.

All Xantia Models are equipped with Hydropneumatic suspension which is self-levelling, the ride height being maintaned automaticly over all road conditions. On the Hydropneumatic system, four spheres, one on each wheel, are filled with nitrogen, which is a gas and therefore can be compressed, providing the "spring" action. From the midle of the year 1993 was anti-sink system SC.MAC (Citroen de Maintien de l'Assiette Constant) added to the rear shaft. This system maintain the car at driving (normal) position while parking.

The spheres act as springs. The link between these springs, and the moving parts connected to the wheels is provided by a liquid, which cannot be compressed.

In VSX the system is added with electronic control. This system is called Hydropneumatic II and it possibles driver to change the hardness of the suspension from confortable to sporty.1. Computer 2. Steering wheel movement and speed of movement sensor 3. Accelerator sensor - reads accelerator movement and rate of movement 4. Brake sensor 5. Speed sensor 6. Body movement sensor 7. Electrovalve 8. Stiffness regulator 9. Extra sphere 10. Front suspension sphere 11. Rear suspension sphere The automatic "normal" position, for a more relaxed ride, and

The automatic "sport" position for more lively sporting driving.



The ride height can be adjust to four different height. The lowest position for loading the trunk

Driving (normal) position

Midle high position for road in a bad state

Maximum height for changing tyres or checking the LHM level

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The SC.CAR (Systeme Citroen a Controle Actif du Roulis) roll limitation system was first demonstrated on the Activa II prototype at the 1990 Paris Motor Show. The system has been fine-tuned to enable the Xantia Activa to corner on the level, thus improving safety and increasing driving pleasure. The system was added to Xantia in 1994. In this system computer control hardness of the suspension by controlling the stabilizerbarrels offset behaviour and valves of the front axle. When the system detects a curve, the on-board computer immediately increases roll stiffness. If the curve continues and the passenger cabin tilts to an angle of 0.3deg, two hydraulic jacks kick in to help restore the vehicle's balance. This possibles to keep the car almost in level when the car enters a bend.See Activa in tests.



1. Steering wheel angle 2. Rate of steering wheel rotation 3. Vehicle velocity A High pressure pump B Anti roll regulator C Electro valve D Regulator E Activa accumulator F Front stabiliser cylinder G Rear stabiliser cylinder H Stabiliser I Suspension computer

At any time, Xantia Activa rolls at most half a degree. This make it not only spectacular to look at, but also improve cornering speed. French magazine L'Automobile tested a Xantia Activa on skidpad and measured an amazing 0.94 g lateral acceleration. This compares competitively with many supercars - NSX managed 0.93 g, Ferrari 512TR 0.92 g, Toyota Supra 0.95 g and Ferrari F40's 1.01 g. This is even more impressive if you consider the Xantia wears just 205/55R15 tyres on this test. Most cars in its class manage around 0.8g only.

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[1992Q45A]

Thats a helluva nice skid pad rating

[rover3l]

yes it you makes you wonder what is making the difference. The active roll is obviously helping but the same effect I don't think was achieved when a Q45 is compared to an active version. Tire tread compound may be a factor also.

[1992Q45A]

It's riding on some puny tires as well

[Q45tech]

"Tire tread compound may be a factor also"

The tire is 95% of the equation...........since the early Q45a all had the same model Michelin Sport XGTV as the basic Q..........any gain was from active and that wasn't much [if any] due to added system weight.

Holding the body level only helps if the suspension is so bad in the first place to not control the tire camber during body roll............a lot less expensive to design and install a good suspension.

[Q45tech]

Also these are tiny light weight [3100 pound] 150 HP cars [0-60=~~9.5 secs] like the Bmw 318-320 [3067 pound] series so a 205/55/15 is plenty of tire!http://www.citroen.mb.ca/Documents/Car/ ... Car/6.html

[louiegz]

Holding the body level only helps if the suspension is so bad in the first place to not control the tire camber during body roll............a lot less expensive to design and install a good suspension.

I wouldn’t say that Citroen is compensating with the active suspension because they have a bad suspension. Citroen have been known for their suspension technology for years. I really don’t care too much about the g numbers, though very impressive for a car like that. What I care about is eliminating roll. I don’t know about you, but when my car starts to roll, I start to back off, well before the limits. I know this is an apples to oranges comparison, but my Q rolls much more that my 330, but when I’m going strait, the Q has the softer ride. This is where the active gives you the best of both worlds. You get the tight, roll free handling with the softer ride on the straits. I know the active suspension didn’t get any extra g’s on the skid pad, but I’m sure it felt more secure on a tight curve that the non active Qs. I’m assuming that the active Q pulled this off well. I’ve never have had the pleasure of driving one.

[elwesso]

I wouldn’t say that Citroen is compensating with the active suspension because they have a bad suspension. Citroen have been known for their suspension technology for years. I really don’t care too much about the g numbers, though very impressive for a car like that. What I care about is eliminating roll. I don’t know about you, but when my car starts to roll, I start to back off, well before the limits. I know this is an apples to oranges comparison, but my Q rolls much more that my 330, but when I’m going strait, the Q has the softer ride. This is where the active gives you the best of both worlds. You get the tight, roll free handling with the softer ride on the straits. I know the active suspension didn’t get any extra g’s on the skid pad, but I’m sure it felt more secure on a tight curve that the non active Qs. I’m assuming that the active Q pulled this off well. I’ve never have had the pleasure of driving one.

Lou just made the best post Ive seen about the purpose of the active suspension.

Id LOVE to see what the active Q could do with some nice wide 17-18in rims with ULTRA sticky tires, and the JDM active controller. I bet it would outhandle a LOT of sports cars.

[1992Q45A]

If you check out the archive threads, where I showed you guys that Toyota Soarer page.

They made it CLEAR the active was the bettet package. The picture of the two cars cornering alone, was reason enough to have the active suspension. The soarer with the active suspension wasn't rolling at all, where as the regular soarer was practically on two wheels.

I'll take active any day

Body roll, Squat, Dive, etc etc is just not sporty

[louiegz]

Also these are tiny light weight [3100 pound] 150 HP cars [0-60=~~9.5 secs] like the Bmw 318-320 [3067 pound] series so a 205/55/15 is plenty of tire!http://www.citroen.mb.ca/Documents/Car/ ... Car/6.html

Good article Dennis. I was amazed to find out that the Active system in the Citroen has a weight penalty of 17kg. If my conversion is correct, that's about 38lbs. I wonder how reliable it is.

[rover3l]

So are we saying that the Q45a was under tired thus the potential of the active suspension was not realized in terms of road holding. With 2004 tire technology might it now be possible to measure an improvement such as Citroen obviously achieved with European tire technology

[louiegz]

So here's something interesting about Citroen I found on their web site.

http://www.citroen.com/CWW/en-...y.htm

For the first time: the lane departure warning system

Innovating in terms of safety, Citroën is making the C5 available with an exclusive system that can detect an unintentional lane change on a motorway or fast road, when the indicator is not activated. A vibrating mechanism mounted in the car seat is triggered on the side corresponding to the direction of vehicle drift to alert the driver who may, for example, be distracted.

Exclusive system? So who came up with it first, Infiniti or Citroen? I think Frenchy did.