Hydraulic circuit sketch with pipe markings (R, PV, Acc, PM) — 1952

A sheet of handwritten sketches from 1952 detailing a hydraulic circuit and several control mechanisms, a milestone in Paul Magès' research on hydraulic gear shifting.

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Presentation and original captions

In 1952, Paul MAGÈS drew the very first sketches of a hydraulic gear shift. A few years later, in 1956, the DS 19 would be equipped with this semi-automatic gear shifting system. Above, 6 sketches of this project.

Understanding this document

In this document

This single sheet brings together several handwritten technical sketches related to a hydraulic mechanism.

The central diagram: hydraulic circuit

The main sketch shows a cross-section of a mechanism, annotated with circulation markings: R (return), PV, Acc (accumulator) and PM, with arrows indicating flow directions p. 4. Parts are numbered 1, 2, 3, 4, associated with the letters AR, E and X p. 4. A spring is drawn at the bottom of the diagram with the indication "1 kg" p. 4.

The connection detail

Top right, a small sketch represents a connection annotated X and E, with red hatching suggesting a flow p. 4. An attached handwritten note, partly uncertain, mentions a "setting to X pipe change" at "neutral" — the reading remains uncertain and cannot be guaranteed p. 4.

The multi-position control

On the right, a cylindrical axis bears a central red circle and an annotation describing "4 position at 90° for 1st 2 3 4", with the mention "provide brake position" p. 4.

The circular diagram and ratchet control

Bottom right, a diagram represents a wheel or drum associated with a "Ratchet Control" operating "90° descending or ascending" p. 4. A nearby mention, uncertain, could suggest the absence of hoses.

Several other inscriptions on the sheet remain illegible or uncertain and have not been included.

Context

This type of sketch is part of the research conducted at Citroën in the early 1950s regarding transmissions and hydraulically controlled gear shifting, a field in which Paul Magès would also develop the famous hydropneumatic suspension. The concepts of return, accumulator and load pressure, typical of automotive hydraulic circuits of the time, recall the principles that would later be applied on a large scale to the DS. These general context elements are, however, not mentioned in the document itself.

Archivist's perspective

This sheet appears to be an exploratory work page, mixing several distinct sketches — hydraulic circuit, connection, multi-position control and ratchet control — probably scribbled during the reflection on the same gear shifting mechanism p. 4.

The presence of numbered markings (1 to 4) and precise values such as the "1 kg" spring suggests a design stage that is already relatively advanced, where certain values are beginning to be fixed p. 4.

This document appears close to other items in the same file, notably the First sketch of a hydraulically controlled gear shift and the Diagram plates P 1214_1 and P 1214_2, which could shed light on the continuation of this technical reflection.