1951 calculation sheet: DS rear hydropneumatic suspension curves

In this document

This single sheet, dated "1951" at the top right p. 1, bears the handwritten header "SUSPENSION HYDRO-PNEUMATIQUE" followed by "TYPE ARRIERE D.S" p. 1.

The main graph

On graph paper, a graph relates the weight suspended on the axle (vertical axis in Kgf, graduated from 200 to 1000, with intermediate markers at 380 and 740) and the suspension travel p. 1.

Several curves are plotted and labelled:

• a central curve associated with the mentions "Transformation isothermique" and "Transformation adiabatique" p. 1;
• two lateral curves noted "correction de hauteur" and "hauteur d'équilibre", on either side of the graph, one apparently corresponding to the "empty" load, the other to the "full load" p. 1;
• a "courbe résultante suspension + butée", indicated by an arrow p. 1.

An annotation also specifies "variation de hauteur qu'il y aurait s'il n'y avait pas de correction de hauteur", which situates the very object of the calculation: to quantify the effect of the automatic height correction p. 1.

The bump stop curve

At the bottom of the page, a separate curve, surrounded by a red line, is titled "courbe de butée seule (à la roue)", with its own axis in Kgf and in travel p. 1. Numerical dimensions accompany this part: two values of "110" and one value of "460" (circled in red), under the mention "course à la roue" p. 1.

One or two underlined handwritten lines appear at the bottom of the page but remain illegible in the transcription; no information can be drawn from them.

Context

The hydropneumatic suspension, developed at Citroën, will equip the DS presented in 1955. The principle is based on spheres containing gas (nitrogen) separated from the oil by a membrane, which allows for automatic vehicle trim correction according to the load — hence the interest, in engineering, in comparing gas behavior according to isothermal or adiabatic laws, two classic physical models of gas compression.

This work of calculation and curve plotting is part of the years of system development before its commercial launch.

Archivist's perspective

This document illustrates, in its raw state, the calculation work carried out by Paul Magès to size the rear suspension of the future DS: confrontation of two thermodynamic hypotheses, consideration of the mechanical bump stop, precise calculation of wheel travel p. 1.

It seems to be a personal work sheet rather than a document intended for distribution, given the medium (graph paper), possible erasures, and handwritten annotations not all of which are decipherable p. 1. Its documentary value lies in the early date of 1951, several years prior to the commercialization of the DS, which attests to design work already advanced on the height correction system.