Note by Paul Magès criticising the Bourcier de Carbon patent on the relaxation shock absorber

In this document

This typewritten note from 18 February 1946 is a technical, point-by-point critique of the Bourcier de Carbon patent concerning a "relaxation shock absorber". In it, Paul Magès comments on several assertions of the competing patent, citing page references.

On the patent's simplifying assumptions

Magès notes that the author neglects tyre elasticity and wheel inertia, which leads him to ignore "wheel tramp" while estimating that "this does not change anything essential to the analysis of the phenomenon" p. 2.

On practical feasibility

Magès is highly critical: if the stated goal — a "total freedom of wheel movement" — were actually achieved, he asserts that "it will be impossible to drive with this device", as wheel tramp would become completely free p. 4.

On the rigidity of spring S

He contests the idea that passing over dips and bumps would maintain "smoothness": as spring S is "4 to 8 times stiffer" than a normal spring p. 8, the resulting rigidity would be much higher than that of an ordinary suspension, degrading comfort on small irregularities ("cobblestones") p. 8-9.

On load behaviour

Magès revisits a point regarding the elongation of the shock absorber when empty and under load: he deems it normal for the energy absorbed to be greater under load, as the period is shorter and the stroke longer, and says he does not understand Bourcier de Carbon's contrary assertion p. 9.

Magès' summary

He concludes that this system "cannot function without 'beaters'" and doubts that the announced smoothness is achieved given the resulting rigidity, while nevertheless recommending: "To be tried all the same".

A handwritten red annotation bears the date "18-II-46".

Context

Bourcier de Carbon was, in the history of the French automobile, a competing engineer who was also exploring advanced suspension solutions at the same time as the research conducted at Citroën by Paul Magès. This note from February 1946 falls precisely within the period when Magès, having joined the design office after his work on the TUB braking limiter (1939-1940), had already drawn the first plans for hydropneumatic suspension on 17 February 1944 and was preparing to conduct, a few months later, the first tests of the 2 CV with hydropneumatic suspension (May-July 1946). These parallel works are part of the immediate post-war excitement surrounding comfort and road holding, which would lead a few years later to the hydropneumatic suspension of the DS (presented on 6 October 1955).

The filing of competing patents and their cross-critical analysis were common in this restricted technical environment, where every engineer monitored alternative solutions.

Archivist's perspective

This document is valuable because it shows Magès not in the process of presenting his own invention, but in a position of technological and critical monitoring, methodically dissecting a rival patent with almost academic rigour — systematic reference to the lines and pages of the source text p. 2-9.

The tone is direct, sometimes ironic ("a mathematician of the calibre of Mr. B.de C."), revealing a pragmatic engineer's mind, wary of theoretical models disconnected from the actual behaviour of the vehicle.

It seems that this note is part of a comparative research phase preceding Magès' later developments on hydraulic systems, traces of which can be found in later documents such as the Technical note: hydraulic transmission of high pressures under short strokes, dated 1948.