Paul Magès' note on the engine-transmission problem (1956)

In this document

The choice of engine and transmission

The note opens with an observation: on congested roads, it is braking and acceleration, rather than top speed, that determine a high average speed "in complete safety" p. 1.

Magès examines three solutions to obtain good acceleration p. 1:

He concludes that the third solution "seems to be the most practical and the most economical" p. 1.

The hydrostatic variator

Magès justifies the choice of a hydrostatic variator: a simple process, already proven "in general mechanics" and transposed by aviation, which must be adapted to the automobile by increasing the power-to-weight ratio p. 1. Regarding efficiency, he acknowledges an uncertainty compared to gears, but insists on the overall engine + transmission efficiency, comparing the envisaged use to that of the "aircraft engine with variable-pitch propeller" p. 1-2.

Braking and other uses of the hydraulic circuit

Good braking assumes brakes that are "constant over time, well-cooled, progressive and powerful", with maximum braking at the limit of adhesion without locking p. 2. Magès proposes direct braking by throttling the oil circulation of the transmission p. 2.

Finally, he lists other uses for the pressurized fluid p. 2: supply for suspension correctors and automatic anti-roll; constant-speed dynamo; ventilation/air conditioning/defrosting; and engine starting via the transmission pump, eliminating the electric starter.

Context

This note dates from 1956, shortly after the presentation of the DS on 6 October 1955, and in the midst of the generalization of hydropneumatics at Citroën — Magès, who joined the design office around 1939-1940, drew up his first hydropneumatic suspension plans as early as 17 February 1944 (Hydropneumatic suspension plans with differential interaction) and conducted the first tests on the 2 CV in 1946 (Notebook of the first 2 CV tests). The comparison with the variable-pitch propeller evokes post-war aeronautical research, from which several automotive engineers were indeed inspired for continuously variable transmissions.

The idea of an entirely hydraulic transmission also irrigating braking, suspension and starting announces, in a general way, the philosophy of the LHS (Synthetic Hydraulic Fluid) which would later unify several assisted circuits at Citroën — but this link remains an external perspective, not established by the document itself.

Archivist's view

This two-page note, annotated "Transmission of movement by hydraulic means" in Magès' hand p. 1, seems to be a preparatory reflection document rather than a completed technical report: the tone is that of an exposition of reasoned ideas, almost a plea for a global hydrostatic solution.

It is striking that the same text links transmission, braking, suspension, electrical supply and starting — a probable sign that Magès was already conceiving, as early as 1956, hydraulics as a single energy serving several vehicle functions, far beyond the suspension alone that made his reputation.

The reference to "throttling the oil circulation" for braking p. 2 would deserve to be cross-referenced with other pieces in the collection mentioning hydraulic braking tests, if such documents exist in the archives.