Gas springs (in most cases U-bellows) are mainly used in buses (fixed entrance height) and trucks (high pay-load in comparsion to unladen weight). A spring element with fully supported pneumatic U-type bellow for a passenger car is shown in the figure.
Apart from level control, a stepless pneumatic damping adjustment is realised in this case (soft characteristic favourable for travelling comfort, stiffer characteristic favourable for driving stability).
A defined contour of the rolling piston influences the spring characteristic by a variation of the effective surface area AW. Additionally, the auxiliary spring (bumper) leads to a steep progressive behavior of the spring characteristic in compression.
The response of a pneumatic spring is influenced particularly by the orientation of the cord angle in the spring bellow. Clear improvements are noticed, when the load carrier is arranged axial to spring direction. However this cord orientation requires an external guidance of the pneumatic spring bellow realised in the form of a supporting tube, in order to be able to compensate tangential forces.