Notebook of the first 2 CV hydropneumatic suspension tests (May-July 1946)

In this document

The notebook and the test car

This school notebook, dated "MAY 1946" on its cover with the mention "1st 2 CV HP Suspension Tests" p. 32, records day-to-day tests of the hydropneumatic suspension on the test car designated "Car B9" p. 33. The logs run from late April to late July 1946 (last notes from 23-24 July, p. 51), with a first mileage mentioned on Tuesday 7 May ("Km 6874", p. 34).

Settings and technical incidents

The notebook details inflation pressures, valve diameters and spring settings, with successive tests at 20, 22, 25, 30 and then 35 Kg/cm² p. 34-40. A table from 14 May summarizes several combinations of pressure, valve diameter and spring setting for the front and rear p. 38.

Seal leaks return constantly: an alpax body showing "a significant blowhole" is replaced by "a simple 120 cm³ bell" p. 33; on 21 May, the changing of the four seals reveals a "deplorable state", the lip being "chewed" due to "lack of lubrication", illustrated by a cross-section sketch p. 41. Several seal models are tested (hard B38, ordinary B8, "graphited E 24" seals, p. 42-51).

Driving impressions

Road tests, notably on the "Longny Circuit" and at Montlhéry, contrast flexibility and road holding: "Steers too much in corners, but perfect suspension in straight line" p. 35. Comparisons are conducted with the "R1" front-wheel drive and a "TPV 500 cm³" p. 43, 49, noting an "indisputable difference" in comfort.

People mentioned

The notebook names Cadiou ("Tests with Mr. Cadiou", p. 39), Lefebvre / "Lefevre" p. 43, 49 and Boulanger ("Tests Mr. Boulanger Cadou Lefevre", on 18 June, p. 49), as well as Legrand and Justo for mechanical monitoring.

Notable innovation

At the end of July, the notebook reports the "Installation of the first experimental anti-roll device - Hand control", accompanied by a diagram and an "Anti. Roll" label stuck on the page, with the note "Shows that correction obeys quickly" p. 51.

Context

The 2 CV is the small Citroën automobile project launched after the war; the hydropneumatic suspension, developed by Paul Magès — who joined Citroën in August 1925 and had already authored hydropneumatic suspension plans as early as 17 February 1944 (Hydropneumatic suspension plans) —, would not ultimately be retained for it but would become the signature of the future DS, presented on 6 October 1955. Boulanger was then leading Citroën, Cadiou and Lefebvre were part of the team of engineers and test drivers. The "R1" mentioned as a comparison reference likely refers to the contemporary Renault 4CV.

Archivist's perspective

This notebook constitutes one of the very first road test logs of the hydropneumatic suspension, a pivotal period where the system is still tested on a small-displacement chassis before being reoriented towards heavier cars — the test of the 15-Six H (3-5 April 1954) attests to this reorientation. It seems that the seal and damping difficulties documented here p. 33-51 directly fed the more theoretical research preserved in the Folder "Theoretical study – hydropneumatic suspension 1943/44".

The appearance, at the end of the notebook, of the first anti-roll device p. 51 marks an important step often associated with the rest of Magès' career, who would continue this work at the design office until his retirement from Citroën in September 1974 (photographs of the retirement). The last pages p. 52-53, closer to a mileage tracking table and a standard tool control sheet, seem to be annex documents inserted into the same notebook rather than a direct continuation of the test log.