Status report of 15 June 1964 on the work of the Citroën Hydraulic Study Group

In this document

This handwritten note, dated "15-06-64" p. 7, provides a comprehensive overview of the projects underway at the Hydraulic Study Group led by Paul Magès.

DS-ID damping and suspension

A new "damping law" allows for "traversing heavy undulations at high speed without losing too much in terms of 'ride smoothness'", with a clear improvement in cornering road-holding p. 7. Its "production" formatting is under study, as is the improvement of suspension links, linked to the increase in loads. The application of an "aperiodic rear cushion" is being considered p. 7. Regarding hydraulic anti-roll, tests are continuing but remain without practical application without a change in the rear axle architecture p. 7.

Headlight correction and steering

An "effective and very simple solution" for automatic headlight correction against pitching movements is described as applicable to the "D61" p. 8. The "power-assisted return" steering is the subject of several assemblies at the B.E.A. and the LABO; the study aims to reduce cost and bulk, and the "too fast return" defect is reportedly resolved p. 8. Tests of differentiated front/rear roll stiffness are being considered to increase "self-stability", as well as an experimental assembly for heavy goods vehicles p. 8.

Transmission, clutch, braking

The hydraulic shifting of the 1st gear synchro and the clutch on the DS are "considerably" improved p. 9. The current hydraulic pressure regulator has an oil overheating defect; a more precise version is awaiting industrialisation p. 9.

Regarding DS/ID braking, a "Slip limiter" is being tested for trajectory control during braking, with results deemed good but implementation not immediate p. 9. The author regrets that the application of rear disc brakes is not a priority, considering the gravity of the problem "not well understood" p. 9-10, and insists on an issue of "precision and consistency of distribution" rather than pure efficiency p. 10.

For heavy goods vehicles, two original servo-braking solutions improve the progressiveness of empty brakes p. 10.

Hydrostatic transmission

Endurance tests are "satisfactory" and "the problems of automaticity are perfectly resolved" p. 10. Monobloc assemblies for 3 CV should allow driving by "early January 65", these components being transferable to a 50 CV engine. For a power of 100-120 CV, prototype plans are expected at the end of January 65, with parts production before December 65 p. 10.

Context

The Citroën Hydraulic Study Group, led by Paul Magès, is the birthplace of the hydropneumatic suspension that appeared on the DS in 1955. In the mid-1960s, Citroën explored applications derived from this hydraulic technology—braking, power steering, self-levelling—which would find a later outlet for some, notably on the SM (Diravi steering) and on later versions of the DS (rear disc brakes, headlight corrector). The hydrostatic transmission, for its part, would remain more experimental.

Archivist's perspective

This document offers a rare and synthetic view of Magès' research activity at a precise moment, mixing completed projects, explored avenues and regrets expressed with a certain frankness, particularly regarding the delay in rear disc brakes p. 9-10.

It seems that several innovations mentioned here—the power-assisted return steering, the headlight correction—foreshadow developments that will be found later, for example mentioned in the Letter from J. Wolgensinger to Paul Magès on the SM steering. Concerns about road-holding and braking also find a later echo in the Handwritten note of 1 June 1970 on limiting rear wheel slip, suggesting a continuity of reflection by the engineer on these subjects for several years.