Citroën Plan E 3091 — Hydrostatic transmission of vehicle L, 2nd generation

In this document

This document is an industrial technical plan from the Société Anonyme Automobiles Citroën, referenced E 3091, concerning the "T.H. of the vehicle L 2nd Generation" p. 2. "T.H." stands for hydrostatic transmission, as attested by the complete title block: "DÉSIGN: Hydrostatic transmission, 2nd generation" p. 2.

The drawing

The plan represents in cross-section a complex mechanical assembly: a housing with several pistons or cylinders aligned in an oblique row, evoking a "barrel" or group of inclined cylinders, as well as two separate sub-assemblies in the lower left part, drawn as cylindrical rods threaded at one end p. 2.

The identification title block

The title block mentions: "DESSIN: Mailocheau", a date "7.3.7[uncertain: 6]", the issuing department "5° B.E.A." and the mention "SOCIÉTÉ ANONYME AUTOMOBILES CITROËN – REPRODUCTION INTERDITE" p. 2. The fields "MATIÈRE", "TRAITEMENT", "REVÊTEMENT" and "POIDS" appear in empty boxes. A handwritten annotation "L 74" appears at the top right of the drawing, accompanied by a barely legible stamp p. 2.

The handwritten date of the title block, although uncertain on the last digit, suggests a "7.3.7[6?]", that is to say potentially 7 March 1976 — but this reading remains uncertain and cannot be affirmed with certainty p. 2.

Context

The "vehicle L" mentioned in this plan corresponds, in the internal vocabulary of Citroën at the time, to a research or development project identified by a letter-code — a common practice for the manufacturer to designate studies before their final commercial name. The acronym "B.E.A." refers to the Bureau d'Études Automobiles (Automotive Design Office) of Citroën, where Paul Magès directed research on hydrostatic transmission from the beginning of the 1960s.

The hydrostatic transmission, an alternative envisaged to the classic gearbox, was based on a principle of power transfer by pressurized fluid between a pump and one or more hydraulic motors, allowing for continuous variation of the gear ratio — a line of research that Magès pursued over several generations of prototypes for more than a decade.

Archivist's perspective

This plan E 3091 seems to document an advanced stage of the hydrostatic transmission program, designated here as "2nd generation", probably subsequent to the work on the GS hydrostatic transmission (1974) and the reflections recorded in the handwritten note by Magès on the "Vehicle L transmission problem" (25 November 1973), which concerns the same vehicle designated by the letter "L".

The presence of the draftsman's name "Mailocheau" and the reference to the "5° B.E.A." p. 2 place this document in the normal production circuit of Citroën design office plans. It illustrates, on its modest but precise scale, the persistence of the hydrostatic transmission project led by Magès until the mid-1970s, in continuity with the folder "Hydrostatic transmission 59-74" which seems to group together all of this long-term research.