Handwritten sketch: first diagram of a power steering system (May 1954)

In this document

First sketch dated 15 May

The page bears the underlined title « Servo-direction » (Power steering) and a handwritten date "15.5.4[uncertain]" p. 1. The main sketch, on the left, represents an elongated mechanism seen in cross-section, with a coil spring depicted in the centre and the letters "D" and "G" repeated on either side of the axis — presumably to distinguish right and left p. 1. Curved tubing connects two superimposed assemblies up to a vertical arrow marked "DIR" p. 1.

A handwritten note accompanies this sketch: the spring mentioned "could be replaced by [uncertain term] block or other (or 2 adjustable to allow variation of flexibility)" p. 1. The idea of adjusting the flexibility of the mechanism by one or two adjustable elements is therefore clearly formulated in the text, even if the exact term remains uncertain.

Supplementary note of 16 May

A second mention, dated "16.5.", refers to a « Direction complètement Hydraulique » (Completely Hydraulic Steering) p. 1, as well as a barely legible note mentioning a "first ascent" and an uncertain term close to "clevier" p. 1.

Other graphic elements

The page contains several other sketches and technical diagrams: a cross-sectional diagram of a hatched element at the top right, two small sketches of the same part seen from two angles, and at the bottom right a framed diagram of a hydraulic circuit with connected rectangles, a zigzag spring, a central circle flanked by two small circles, and tubing leading to a rectangular box p. 1. These elements are not accompanied by any usable legend.

The sheet was written on the front of a pre-existing printed document of a tabular nature, the text of which shows through but remains illegible p. 1.

Context

In the mid-1950s, Citroën engineers, including Paul Magès, were developing the principles that would lead to hydropneumatic suspension and, more broadly, to the hydraulic services of the future DS (presented on 6 October 1955): power steering, braking, suspension. Magès, who joined Citroën in August 1925 and was then deputy head of Super-Control after his time in the design office from 1939-1940, had already carried out the first hydropneumatic suspension tests on the 2 CV in 1946 and on the 15-Six H in April 1954 (15-Six H test), only a month before this sketch. The notion of "servo-direction" refers to the assistance of the driver's effort at the steering wheel by a hydraulic device — an innovation then emerging in the automotive industry, which is part of this same research dynamic.

This general context is not mentioned in the document itself: it only serves to situate the sketch in its era and in Citroën's research on hydraulic circuits applied to driving.

Archivist's perspective

This sheet appears to be a very early working sketch, in pencil, taken "on the fly" — two close dates (15 and 16 May) suggest continuous reflection over a few days, with a notable evolution: from the search for a flexibility adjustment by spring or block p. 1 to the idea, the following day, of a "completely hydraulic" steering system p. 1.

It is probable that this document captures a pivotal moment of reflection, where Magès is still exploring several mechanical avenues before converging towards an all-hydraulic solution. The presence of multiple sketches and variants on the same page reinforces this hypothesis of a research draft rather than a finished plan.

The recycled support (a tabular printed document reused on the back) is also revealing of the engineer's working habits, who seems to have noted his ideas on the first paper available.