Rolls-Royce / Citroën interview of 18 March 1963 on the hydraulic braking circuit

In this document

The participants

This typewritten report recounts an interview on 18 March 1963 at 4 p.m. between representatives of Rolls-Royce (S.V. Massey Crosse, B.R. Shilton, M. Harries) and Citroën (Paul Magès, Etievant, Henry-Biabaud) p. 29.

The official subject is presented immediately: "requests for information from Rolls-Royce concerning the dust-tightness of the spools and valves of the hydraulic braking circuit" p. 29.

Sealing and ball valves

Rolls-Royce mentions its difficulty in keeping the fluid clean, fearing that dirt might prevent the ball valves from closing properly. Magès replies that the vehicle's vibrations cause the valves to unseat even in the presence of some dirt, and specifies that the relative "ball/orifice" dimensions as well as the support spring force are defined experimentally. The ball size used by Rolls-Royce is given: "0.05 inch" p. 29.

The sketches drawn by Shilton to explain the Rolls-Royce braking system convince the Citroën interlocutors that the two devices are "quite similar," except for the part specific to braking (cylinder, etc.) p. 29-30. Rolls-Royce cleans its parts with methylated spirits; Magès deems everything that contributes to cleanliness desirable p. 30.

Bleeding, manufacturing and seals

Magès explains the brake bleeding method (lowering the pressure pump to 0), a method already present in the Citroën network's repair instructions p. 30.

Regarding the manufacturing of delicate parts, Citroën replies that the machines used are "original" and fall under "manufacturing secrets"; Magès specifies that at the start, delicate operations were done by hand. Rolls-Royce indicates that it proceeds, for its part, by grinding and lapping p. 30.

Rolls-Royce plans to systematically change the seals every 70,000 km p. 30.

Vibrations and patent license

Shilton reports vibrations in the hydraulic system during braking; Magès attributes this to a spring interposed between the control button and the balance beam, and suggests a test with the Citroën control assembly p. 30.

The report concludes that this interview could only have taken place due to a "probable transfer" of a Citroën patent license to Rolls-Royce, without any question of technical assistance. Shilton must report to his management, as Rolls-Royce intends to manufacture its own hydraulic circuits p. 31.

Context

The hydraulic braking system mentioned here is the high-pressure one developed by Citroën for the DS from 1955 onwards, inseparable from the hydropneumatic suspension invented by Paul Magès. Rolls-Royce, a prestigious British brand, was interested in this technology for its own models at the time, which explains the patent license exchanges between the two manufacturers in the early 1960s — an industrial rapprochement that is known but whose precise terms remain, outside of this document, to be documented.

Archivist's perspective

This report, probably written by Etievant, offers a rare glimpse into confidential technical discussions between Citroën and a prestigious competitor, in a context of patent transfer rather than technical collaboration — a nuance that Citroën is keen to emphasize p. 30-31.

One can perceive Magès's caution regarding manufacturing questions, which he qualifies as "secrets" p. 30, revealing the strategic importance given to the industrial know-how of the hydraulic circuit.

This document is in line with the concerns regarding the safety and reliability of hydraulics already addressed in note BEA 43.027 on the operational safety of hydraulics and in the investigation into hydraulic leaks of the DS 19, which show that the issue of sealing was a sensitive subject for Citroën itself at the time.