Paul Magès' note on the braking of the DS 19 (2 April 1958)

In this document

This handwritten note, dated 2 April 1958 and signed by Magès, sets out a technical reflection on the braking of the DS 19 p. 270.

Existing braking circuits

Magès first describes the separate front and rear brake circuits, each equipped with an accumulator of approximately 0.4 litres (gas + liquid), inflated to 40 kg/cm² p. 270. He details the volumes of liquid available according to pressure:

p. 270

The idea: using the suspension spheres

Magès then proposes using the suspension spheres as a safety reserve for braking. For the front suspension (2 spheres of 0.750 l, inflation 60 kg/cm²), the volume of liquid available is 550 cm³ empty (equilibrium pressure 95 kg/cm²) and 680 cm³ loaded (110 kg/cm²), plus approximately 50 cm³ linked to the car's settling p. 270. For the rear (2 spheres of 0.750 l, inflation 26 kg/cm²), he notes 750 cm³ empty (52 kg/cm²) and 1110 cm³ loaded (100 kg/cm²), with the same 50 cm³ addition p. 270.

He concludes that "the braking energy reserve is therefore more than doubled" by exploiting the suspension spheres p. 270, and emphasizes that "the lack of suspension forces the driver to stop or drive very slowly" — a warning more effective, according to him, than the best electric horn p. 270. Finally, he links the suspension pressure, proportional to the weight carried by each axle, to the necessary braking torque, seeing this as a path to solving what he calls the "number one problem" of the automobile p. 270.

Context

The DS 19, launched by Citroën in 1955, is renowned for its hydropneumatic suspension, an invention of Paul Magès, who joined Citroën in August 1925 and whose hydropneumatic suspension plans date back to 17 February 1944 (Hydropneumatic suspension plans with differential interaction). Historically, this system effectively served as the basis for brake assistance on Citroën vehicles with spheres (DS and subsequent models), where the hydraulic pressure of the suspension powers the brakes — a feature that would become a technical signature of the brand. This note is therefore situated at a key period in the development of the DS, a few years after its commercial launch and while Magès, a self-taught man who became deputy head of Super-Control, continued the development of his invention within the design office (autobiographical notes).

Archivist's perspective

This document offers a valuable insight into Magès' engineering reasoning: he seeks, through calculation, to justify the extension of his own invention (the suspension) to a new function, braking p. 270. The formula regarding the "number one problem" of the automobile testifies to the ambition he held for this solution, he who would dedicate 49 years of his career at Citroën to its perfection, from his arrival in 1925 until his retirement in September 1974 (photographs of the retirement).

This sheet belongs to the same file as the Summary of folder 41-59, dedicated to the hydropneumatic suspension and its developments on the DS — a context consistent with this 1958 technical note.