More details emerge of Citroën's new “hydraulic cushion” suspension

  • 20-Jun-2016 03:54 EDT
Citroen damper unit.jpg

It is known that secondary dampers which Citroën engineers call “hydraulic cushions” complement the regular shock absorber and springs of each suspension unit. The dampers work progressively, one for rebound, a second for compression, positioned at the upper and lower extremes of each a unit instead of conventional bump stops.

First details are emerging of Citroën’s new vehicle refinement package including an innovative suspension system, the existence of which was revealed by AE late last year; see http://articles.sae.org/14498/.

At that time, Citroën CEO Linda Jackson said of the still secret program: “The technology we are developing will deliver what I call the ‘Citroën ride.’” Since then the Advanced Comfort Program has moved toward production. It uses secondary dampers that Citroën quaintly refers to as “hydraulic cushions” to complement the regular shock absorber and springs of each suspension unit.

The dampers work progressively, one for rebound, a second for compression, positioned at the upper and lower extremes of each a unit instead of conventional bump stops. They should deliver better control throughout much of the suspension’s travel.

The new suspension is designed to be cost effective and applicable across Citroën’s model range. When it becomes available, possibly early 2017, it will mean au revoir to the relatively complex and expensive oléopneumatique systems that started with the ground-breaking 1955 DS and that are still used on some current versions of the C5.

Striving to reduce system cost

Citroën chassis engineers are refining the system on a Cactus test vehicle together with other complementary technologies to provide an integrated, holistic approach to smoother, quieter travel. More than 30 patents have been applied for, which means Citroën engineers are being a shade diffident about its design and development of the new system.

But what they are saying is that in instances of what it terms “slight compression and rebound,” springs and shock absorbers work together to control vertical movement without need of the “cushions.” But in “more significant” compression and rebound situations, springs and shock absorbers then work together with the “cushions” at suspension travel extremes gradually slowing movement, absorbing and dissipating energy, whereas typically, regular bump stops absorb energy suddenly and then partly return it.

Jackson said that if manufacturing costs can be met the new suspension’s use will be extended across Citroën’s car range, even to the little C1. This would mean the end of  oléopneumatique. But it is not a standalone technology to smooth Citroën’s future. Said Jackson: “Comfort is not just about suspension; it also encompasses seats, storage and the way you drive.”

Going big on adhesive bonding

So when the suspension has completed its subtle damping, the bodyshell then enters the picture. Body stiffness figures have risen rapidly and hugely for almost all cars in recent years and Citroën believes that its use of structural bonding will take this further.

It is developing an “industrial process” specific to the company to bond structural parts using a discontinuous line of adhesive with an electrical weld point used only if the line is interrupted.

Citroën refers to “significantly greater overall body rigidity” being achieved – typically some 20%, a huge improvement over what is already in production and that should achieve a very considerable reduction of vibration. There will also be cost and weight benefits, with the reduction in electrical welds required.

Seating is another complementary area to improve comfort. Comfortable seats have long been a Citroën forte but now memory foam, a la mattresses, are set to play a role, shaping to an individual passenger’s body contours. Materials used include polyurethane foam and viscoelastic or textured foam.

The company has improved acoustic comfort and reduced vibration in recent models, including the latest C4 Picasso, which uses the PSA (Peugeot Citroën) Group’s EMP2 platform, via damping of the front subframe and use of a dual-material acoustic shim for the rear suspension.

All of these development programs are incorporated in the test program Cactus. Depending on development program advances, including further patent applications, Citroën may release more information on its advanced comfort program at the 2016 Paris Motor Show in September, and some elements of the technologies will appear sooner rather than later.

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