Citroën’s Hydropneumatic Suspension Made Rides Smoother (With A Catch)

French carmaker Citroën by no means reached the identical degree of worldwide success as its rivals in neighboring Germany and Italy, and it might not be a well-known identify to American readers. Maybe it isn’t a shock, then, that its most revolutionary invention by no means caught on in different automobiles the world over. And but, it is nonetheless in use across the globe, and you will have even been on one thing that makes use of it, with out realizing it.

This know-how is hydropneumatic suspension, which discards conventional leaf springs and coil struts in favor of fluid dynamics. Briefly, the system makes use of the truth that a gasoline may be compressed, however a liquid cannot. With every wheel linked to a liquid-filled piston, every bump within the highway would push that liquid up right into a gas-filled sphere. Whereas the gasoline would compress, its stress would enhance because it did so, pushing the liquid again down once more and, thus, the wheel.

That made for a legendarily easy journey, vastly exceeding the rest in the marketplace when it comes to sheer consolation. Even drives alongside rocky terrain felt like crusing on a cloud. However a number of essential flaws dragged the system again all the way down to earth. Within the early days, the liquid had a bent to rot, which is not ultimate for, properly, something. Later liquid mixtures solved that difficulty, however even then, the system was sophisticated, which made it costly – one in all a enterprise’s least favourite issues.

The guts of the system is its spheres, which maintain the liquid and the gasoline. The engine is used to pump within the liquid to the quantity needed to attain the specified stress. There’s one sphere for every wheel, one to be a holding tank for the liquid, and (in some automobiles) one to be a devoted holding tank for the brakes. Why would you want one for the brakes? Properly, along with being the suspension, this technique is also used to function the brakes in addition to the clutch, gear change, and even steering.

As a result of the liquid was being actively pumped out and in (to maintain the stress from the compressed gasoline on the desired quantity), the hydropneumatic system allowed for a wildly bigger vary of suspension firmness than every other system thus far. Completely comfortable at low pace, a lot stiffer at excessive pace. The automotive might additionally self-level, even when beneath load or on an uneven or sloped floor. You could possibly elevate or decrease the automotive at will. It really is a exceptional system, introduced down by its sheer complexity and expense.

Hydropneumatic suspension was the brainchild of Paul Mages, who developed prototypes for Citroën all through the Forties and ’50s. It debuted on the market because the rear suspension within the 1954 Citroën Traction Avant, and a 12 months later as the only real suspension in the Citroën DS, a automotive that made it cool to be bizarre. Within the latter’s public unveiling, the person behind the wheel was Mages, having fun with his, and his invention’s, second within the highlight.

Over the next a long time, the fluid suspension system can be a signature of Citroën and a serious advertising and marketing level for the corporate. Different firms, similar to Mercedes and Toyota, would ultimately showcase their very own variations. Rolls-Royce, ever seeking a extra luxurious expertise for its drivers and their passengers, even licensed Citroën’s system for the Silver Shadow.

Most of that has light away with time, nevertheless, and almost all automobiles use coil struts today (although some SUVs and most vehicles use leaf springs). Even Citroën is abandoning its personal achievement: The Citroën C5, which ended manufacturing a number of years in the past, was the final mannequin the French carmaker produced with the know-how.

Within the early days, Citroen used a fluid that may rot the entire system if water acquired into it. By the Sixties, nevertheless, an improved chemical combination eradicated this difficulty. Nonetheless, as a result of the liquid was being pumped by the engine, that meant horsepower that would in any other case be used for pace was as a substitute being utilized by the suspension, an issue that coil springs haven’t got.

However the greatest difficulty with hydropneumatic was merely that it was costly. The complexity of a machine that routinely pumps liquid in the appropriate quantities is way greater than, say, a easy metal coil. In later a long time, Citroen was putting in the system on fewer automobiles anyway, so few that economies of scale had been being misplaced which, once more, elevated prices. 

By 2015, Citroen threw within the towel, asserting that it will be leaving its signature invention behind. Nonetheless, even when Citroen does not use the system anymore, it isn’t gone fully.

Regardless of the top of its recognition in passenger automobiles, hydropneumatic suspension is definitely nonetheless in extensive use at the moment. In truth, should you’ve ever flown on an airplane, you’ve got skilled it your self. That is as a result of almost all plane use oleo struts, a type of hydropneumatic, on their touchdown gear.

The identical may be stated for army tanks, that are simply concerning the heaviest kind of car you may roll alongside the bottom. The crew wants a suspension system that may hold them from breaking their bones even when powering by the planet’s roughest terrain. Simply as essential is the system’s self-leveling potential, which may hold the cannon regular even when on the transfer over uneven surfaces. Since a tank’s major job is to, you recognize, goal at issues, that is a fairly essential function.

And should you completely should have this technique for your self, it’s truly nonetheless obtainable for shoppers at the moment. Mercedes’ modern-day E-Energetic Physique Management suspension is a hydropneumatic system, at the moment obtainable in higher trims of the S-Class sedan and the GLS580 and GLS600 Maybach SUVs. Simply so you recognize, Mercedes does warn: “System can not overcome the legal guidelines of physics, neither is it an alternative to taking note of driving, site visitors and circumstances.” Ah properly.