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All Tests
F7 F9

Hydropneumatic Suspension

Nitrogen (light blue) provides for particularly sensitive responding of the suspension in combination with the advantages of a level control system. In comparison to steel springs, the induration is considerably smaller, and the distance towards the roadway remains the same, regardless of the amount of load. The travelling comfort seems to be endless. Additionally, the headlight levelling becomes obsolete, as well as the mechanical or hydraulic jacking equipment. Interestingly, in 1954 the hydro-pneumatics was first used, at the rear axle of the Citroen 15 CV.

The hydraulic pneumatics suspension resembles the gas pressure absorber. Also modern air suspensions copy functions that are already present for quite some time with this technology.Taking the small air space of the single-tube shock absorber into mind, enlarging and replacing it by a larger nitrogen area, exchanging the separator piston for a diaphragm and connecting the absorber oil area to a hydraulic system (e.g. the power steering), makes the suspension function hydro pneumatically. The gas is elastically, and its effect can be adjusted by the inflow or discharge of hydraulic oil. However, the continuing co-operation of a hydraulic pump and a thought out regulation are essential. After scarcely 50 years it has finally found its way to other car manufacturers, being more reliable in service and with an electronic regulation.

Picture 1/2

The hydraulic pump pumped only little oil to the ball, because the vehicle is nearly completely unloaded. The diaphragm curves to the right and the area filled with nitrogen is very large. When the spring is engaged, the right valve in the absorber piston opens and fully absorbs the job. The diaphragm is shifted a little to the left. When the spring is being released, the diaphragm moves exactly opposite. The diaphragm is moved back to the right. The left valve in the absorber piston opens and absorbs more strongly (traction phase).

Picture 3/4

The vehicle is loaded up to the permissible pay load. Nevertheless the absorber to the right shows no difference. The procedures for engaging and disengaging are exactly the same as in fig. 1/2. The only difference is that the system pumped hydraulic oil into the ball, increasing the preload of the nitrogen. The diaphragm still changes little when engaged or disengaged, however, its overall position has strongly shifted to the left and is thus in a completely different position.


If the brake is integrated into the hydraulic pneumatics suspension, the vehicle should be towed away exclusively with a running engine.

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