“New Trends in Using Air Suspension” — British article citing the Citroën cylinder (July 1959)

In this document

This article, published in July 1959 in the British journal Engineering Materials and Design, is signed by K. E. Nicholds, an engineer at the company Hymatic Engineering Co. Ltd p. 30. It offers a technical synthesis on air suspension intended for automotive designers.

Physical principles

The article first establishes the theoretical foundations: axle movement relative to the chassis, natural frequency, shock transmissibility, and the concept of “rising rate” — a stiffness that must increase with the load to offer constant comfort regardless of the load p. 31. Several types of springs are compared (leaf, coil, torsion, rubber, liquid springs), with the air spring being presented as the one possessing “inherently the characteristic required” p. 31.

The four types of air springs

The author distinguishes four families of systems p. 31:

1. The piston-cylinder, deemed impractical (sealing problems);
2. The Citroën hydraulic cylinder, where “the oil pressure is communicated via a membrane to a sealed gas-filled vessel”; the article notes that this system allows for ride height control by regulating oil volume, but that a constant frequency cannot be obtained over a wide range of loads because the gas volume varies p. 31;
3. The double-convolution bellows (Fig. 2, 12);
4. The “rolling lobe air spring” (Fig. 8, 13).

Installation and control

Pages 33 to 35 detail the air supply (compressor, reservoir), leveling valves (“non-delay” and “time delay valves”), and open/closed exhaust systems p. 33-35. The article mentions concrete applications: the Leyland chassis supplied to the Dutch railways (Fig. 10, p. 33), a Guy commercial chassis (Fig. 11, p. 33), and the pedestal profile of the 1958 Pontiac designed “using an I.B.M. computer” p. 33.

Conclusion of the article

The author considers a generalization of air suspension on the average car unlikely, but highlights its interest for vehicles with a high load variance (heavy goods vehicles, coaches) p. 35. A bibliography of SAE and Inst. of Mech. E. closes the article p. 35.

Context

At this date, Citroën had launched the DS (1955), equipped with the hydropneumatic suspension designed by Paul Magès. This system, based on oleopneumatic spheres, was then a technical reference observed by the British and American industry, which was developing air suspensions in parallel for heavy goods vehicles and luxury cars (Cadillac, Buick, Oldsmobile — cited in the bibliography).

The stamp “Laboratoire Physique, 27 OCT. 1959” p. 30 suggests that this article was received and archived by a Citroën technical department, probably for competitive intelligence purposes.

Archivist's perspective

This document does not originate from Paul Magès but from a British technical journal; it is of interest for documentary monitoring: it shows how, as early as 1959, the Citroën cylinder was cited abroad as an alternative — and limited — solution compared to air springs p. 31.

It seems that this archive belongs to a comparison file between air suspension and hydropneumatic suspension, conducted internally at Citroën during the same period, as evidenced by the handwritten cover page “M. Bongrand — Suspension à air, 59-61” and the B.E.A. meeting record of 17 January 1961 comparing air and hydropneumatic suspension.

The article, by pointing out the limitations of the Citroën system regarding the maintenance of a constant frequency p. 31, likely fueled internal reflections aimed at defending or refining the hydropneumatic solution in the face of competition.