Handwritten note of 24/6/1959: capacity per side or per axle, effects on pitch and roll

In this document

This handwritten page dated "24/6/59" p. 8 presents a synthetic comparison between two ways of organizing the air capacities of a hydropneumatic suspension:

Capacity per side

According to the note, this setup "increases [the] pitch flexib[ility]" and "reduces [the] roll flexib[ility]", while remaining "identical in 'Pumping'" compared to the other solution p. 8.

Capacity per axle

Conversely, this second setup "reduces [the] pitch flexib[ility]" and "increases [the] roll flexib[ility]" p. 8.

Cornering behavior

An annotation mentions the case of a right turn ("D"): "The pressure increases in L and decreases in R" (left/right sides), with the idea of "taking advantage of the [...] difference at P to move the thrust" — a partially illegible passage p. 8.

Diagrams

The page includes a symmetrical hydraulic diagram in pencil (blue cylinders connected by piping to four red/grey elements, two pairs of actuators) as well as two cross-sectional diagrams of a distributor or valve-type device, one captioned "in a straight line", showing the flow entry via "L" and "R" and, for one of the two, an additional vertical arrow p. 8.

Context

This note is part of the work carried out at Citroën by Paul Magès — who joined the company in August 1925, worked in the Super-Control department and then the design office from 1939-1940 (autobiographical notes) — on the hydropneumatic suspension, the plans for which with differential interaction date back to February 1944 (plans of 17 February 1944) and which would notably equip the DS presented on 6 October 1955. The choice of associating air capacities per side or per axle is a classic question in the design of suspensions with correctors: it determines the distribution of forces between pitching ("pitch"), roll when cornering, and overall vertical behavior ("pumping").

These general concepts of compensated pneumatic suspension were the subject of technical reflections in the specialized press at the same time — although it is not possible here to attribute a precise source to the document other than Magès's handwritten reasoning.

Archivist's perspective

This sheet appears to be a quick working note, almost a comparative aide-mémoire, rather than a formalized report: the telegraphic style, the highlighted pencil diagrams, and the crossed-out passage suggest an ongoing reflection, probably intended to decide between two air circuit architectures p. 8.

It is part of a close sequence of work on this same subject: a note from the same day specifically addresses the "capacity per axle" case with calculation of pressures when cornering, and a note from 29 June 1959 resumes the capacity per side / per axle comparison a few days later — which confirms that this is a followed calculation file, conducted in 1959 in the direct continuity of the work begun as early as 1944 on the hydropneumatic suspension.