Sketch of the disc brake block (HP inlet / return) — DS19 file, 1955

Handwritten sketch of a disc brake block (moving pad, disc, caliper) with its high-pressure inlet and return hydraulic circuits, from a 1955 file on DS19 braking.

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Presentation and original captions

In February 1955, Paul MAGÈS put his reflections on braking down on paper. Long before, in January 1942, he had imagined, in order to distribute braking according to the load on the axles, and thus to avoid untimely wheel locking, controlling the front and rear braking circuits of a PUD7, by means of 2 master cylinders, the control of which was carried out by means of a carriage, the application point of which varies according to the load on the rear axle. Many years later, he would apply this solution for the braking of the DS 19.

Understanding this document

In this document

This page is a handwritten technical sketch titled "BLOC DE FREINAGE" (brake block) p. 4.

The disc brake

The drawing at the bottom left represents a disc brake assembly with its labeled elements: moving pad, disc, and caliper p. 4. A pipe connects this caliper to the central block.

The hydraulic circuits

The central diagram shows a symmetrical mechanical block, with two lines repeated on either side: a "Retour" (return) line and an "Arrivée H.P" (high-pressure inlet) line p. 4. A section marked "X X" is indicated on the component at the top left, likely referring to a detailed cross-sectional view of the device p. 4.

Other elements shown

Also visible on the right is the diagram of a sphere (accumulator) associated with a housing and a rod and articulated lever system, connected by a pipe to the central block p. 4. The exact nature of this sub-assembly is not labeled and therefore remains unspecified.

Context

This sketch belongs to a 1955 file dedicated to reflections on the braking of the future DS19, whose official presentation took place in 1955. At Citroën, engineer Paul Magès was developing at that time the hydropneumatic system that would power the vehicle's suspension, steering, and braking, via a high-pressure pump and accumulator spheres — which the presence of a sphere in this diagram evokes, without the document explicitly naming it.

The disc brake, still uncommon on production cars in France at that date, constitutes a major innovation that the DS would help to popularize.

Archivist's perspective

This sheet appears to be a working diagram intended to visualize the circulation of fluids (high-pressure inlet, return) in a disc brake block, likely in support of a broader reflection on braking presented in the Note "Reflections on braking" in the same file.

The presence of a sphere and a lever system suggests a possible link with the braking distribution or correction mechanisms studied by Magès during the same period, of which a more formalized trace can be found in the Citroën plan: brake distributor and its control.

The average legibility of the page, marked by signs of aging of the medium, invites caution regarding the interpretation of certain unlabeled details.