Incident on the ELV.238 test car with hydraulic suspension (23 November 1951)

In this document

This is a report dated 23 November 1951, issued by the André Citroën Laboratories (53, rue Balard, Paris), referenced "Test No. 220.501", under the heading "PVS - ELV.238 - Hydraulic suspension (Endurance results)" p. 80. The document is addressed to Paul Magès, whose name is noted in handwriting under "ETUDES -" p. 80.

The observed incident

After approximately 43,000 km of endurance testing, the ELV.238 car, equipped with a rear hydraulic suspension, showed "loud squeaking at the rear right", appearing to originate from the suspension cylinder p. 80.

Upon disassembly, the lower support point of the cylinder — normally flat on a new part — was found to be hollowed out by the sphere on which it rests, with an indentation 9/10 mm deep, accompanied by cracks on the edges of the hole and pitting at the bottom. The upper support point, which oscillates little, only bears a simple impression of the sphere p. 80.

The laboratory specifies that there was neither gravel nor lack of lubrication in the support housings, and concludes that the wear occurs "when the relative movement is too great, the metals in contact are not sufficiently hard, or the unit pressures are too high" p. 80. A note indicates that the part was sent to the Metallurgical Department for examination p. 80.

The protective skirt

The report also notes heavy wear on the lower protective skirt of the cylinder, "thickness reduced almost to zero" in places, with deep vertical scratches attributed to gravel trapped between the two skirts p. 80. Two corrective paths are proposed: improving the centering of the skirts or increasing their clearance; complete protection by a rubber bellows is suggested as a "good if not essential" solution p. 80.

A handwritten annotation in pencil specifies "Long type cylinders" p. 80.

Context

This piece is part of the endurance test campaigns conducted by Citroën at the turn of the 1950s to validate the reliability of the hydropneumatic suspension before its industrialisation, which would culminate on 6 October 1955 with the DS. Chronologically, it is situated between the first hydropneumatic suspension plans of 17 February 1944 (Hydropneumatic suspension plans with differential interaction) and the first tests of the 2 CV in May-July 1946 (Notebook of the first tests of the 2 CV with hydropneumatic suspension), before the test of the 15-Six H on 3-5 April 1954. The acronym ELV likely refers to a laboratory test vehicle; this type of numbering and the extent of the mileage covered (tens of thousands of km) are characteristic of the manufacturer's endurance protocols at the time, where Paul Magès — who joined Citroën in August 1925 and was then a technical writer and later deputy head of the Super-Control (Draft letter from Paul Magès to Mr. Sarre) — held a central role in the design office.

Archivist's perspective

This report concretely illustrates the iterative mechanical development work that Paul Magès and his teams were engaged in well before the commercial release of the system: a simple defect in hardness or sphere-plane contact, revealed by a mileage test, leads here to engineering reflection on materials and sealing p. 80.

It seems that this document belongs to a larger technical development file, as evidenced by other items in the same collection devoted to plans and notices from the years 1943-1946, notably the Hydropneumatic suspension cylinder plan — stroke 100, S = 8 cm² and the Summary of folder 41-59, which specifically mention the developments of the hydropneumatic suspension and the rubber used in its protections.