Note of 11 September 1959: hydraulic or pneumatic suspension and the Bougeard patent

In this document

A defended principle: all-hydraulic

The note first establishes the principle of the hydropneumatic suspension as developed at Citroën: "a constant weight of gas, and transmission of all forces by a liquid" p. 4. The authors claim work by "Messrs. MAGES, MERCIER" on longitudinal and transverse interactions, anti-roll, progressive damping and self-levelling p. 4, and state they are "on the right track" p. 4.

The competing solution: pure pneumatic

The text describes an "other principle" where the gas, at variable weight, transmits the forces itself, without liquid p. 4. It recalls that this principle has already been tested "on passenger cars by the Americans" and on trucks by several countries (English, Germans, Italians, French), with a finding of limited "failure" on the passenger car side and "concerns" on the truck side p. 4. A third hybrid path (variable gas + hydraulic transmission) is mentioned as not yet applied p. 4.

A comparative study program

The author — signed M. Cadiou p. 6 — proposes a two-part program: a theoretical part (diagrams, analysis, critique of each system) and a practical part (study of achievements, documentation, tests, endurance, price) p. 5. He requests an engineer to lead it, supported for the theory by "Messrs. MAGES, MERCIER, HONDET, and the Laboratory" p. 5.

The issue of the Bougeard patent

The conclusion of this study is deemed essential "to take a position on the BOUGEARD patent", even if the test of the car concerned is satisfactory, because adopting this path would mean abandoning hydraulics for pneumatics p. 6. The note estimates the necessary studies at "at least 5 years", and mentions the conversion of the Asnières factory to manufacture compressors and air devices, as well as the retraining of after-sales services worldwide p. 6.

Context

The Bougeard patent designated, in the history of Citroën, a competing pneumatic suspension solution examined at the end of the 1950s — a period when the brand was refining the hydropneumatic suspension of the DS, launched in 1955. This internal debate illustrates the technological hesitations that preceded the generalization of the hydropneumatic system on subsequent models (ID, GS, SM, CX).

Archivist's perspective

This document sheds light on a pivotal moment: Citroën is seriously questioning the possible abandonment of the hydropneumatic path in favor of a competing pneumatic solution, even though Magès and Mercier are its architects p. 4-6. The numerous handwritten annotations in red — question marks on "MERCIER", braces, exclamation marks — suggest a critical reading, probably by Magès himself, as the issue directly affects his work.

The follow-up to this debate does not appear in the document, but the Summary of folder 60-74 and subsequent exchanges on hydraulic safety, such as note BEA 43.027, show that the hydropneumatic path was indeed maintained and deepened in the following years.