Note of 20 March 1963: Citroën/Rolls-Royce meeting regarding a hydropneumatic suspension licence

In this document

The meeting

The minutes, dated 20 March 1963, relate a meeting on 18 March 1963 between representatives of Rolls-Royce (Messrs. Massey Crosse, Shelton, Harris) and Citroën (Messrs. Henry-Biabaud, Magès, Etiévant), devoted to a potential licence for the Citroën hydropneumatic suspension patent p. 32.

Filtering and fluid cleanliness

The discussion opens on the elimination of dust suspended in the fluid. Citroën specifies that filtering is done "on 6/100 nylon mesh", as finer filtering leads to clogging; this level is deemed sufficient given the spools used. Cleaning of parts can, in certain cases, involve ultrasound ("high frequency") p. 32.

Valves, tolerances and leaks

Ball valves require careful adjustment of the ball/seat circle diameters; a ball diameter of 3 mm is considered "a bit small" by Citroën. The dimensional tolerance of the spools is set at 0.5 μ, including all form defects. An order of magnitude for leaks of 15-20 cm³/hour is presented as "normal" p. 32.

Dashpot, spools and piping

The pulsating pressure regime and spool damping refer to the adjustment of the dashpot; Citroën proposes to try "a Citroën block with direct pedal". No seizing of the spools has been observed, nor have any failures or ruptures of piping been reported, provided that suitable fittings and correctly reserved elasticities are used p. 33.

Pump, fire and maintenance

To the question of the cost of the seven-piston pump, Citroën replies that it has sought to modify it, referring to a single-piston pump on the "ID I9". The risk of fire was feared but no incident occurred. A revision interval for rubber parts at 70,000 km is considered correct by Rolls-Royce p. 33.

Spool finishing and follow-up

Spool edges must remain sharp to stop dust and prevent jamming; Mr. Shelton notes having observed a "slightly serrated" edge on a Citroën spool. The factory visit is avoided. The meeting concludes that any technical assistance agreement would require a prior agreement between the two managements p. 33.

Context

Rolls-Royce, at that time, was interested in the hydropneumatic suspension technology developed by Citroën for the DS, in a logic of licensing or technical partnership — an approach consistent with the reputation for innovation of this system in the automotive industry of the 1960s. This context remains external to the document, which does not detail the commercial outcomes of the negotiation.

Archivist's perspective

This document is valuable because it provides a rare glimpse of the external view taken of the industrial development of the Citroën suspension: the questions from Rolls-Royce (filtering, tolerances, dashpot, pump) betray an expert attention to manufacturing details p. 32-33.

It seems that Magès, present at this meeting, had to defend technical choices that were already old (spools, valves, multi-piston pump) in the face of an interlocutor concerned with reliability and cost. The reference to a single-piston pump on the "ID I9" suggests a reflection on evolution in progress p. 33.

This document is part of a series of internal notes on hydraulic reliability from the same period, such as Note BEA 43.027 on the operational safety of the hydraulics or the investigation into hydraulic leaks of the DS 19, which shed light on the reliability concerns mentioned here by Rolls-Royce.