Endurance test report for the PVL ELV.324 hydraulic suspension (6 March 1952)

In this document

This document is a report from the André Citroën Laboratories (53, rue Balard, Paris), addressed to Mr. Magès, referenced "TEST No. 220.652" and dated 6 March 1952, concerning the endurance results of the hydraulic suspension of the test vehicle P.V.L. ELV.324 p. 95.

The incident observed

After approximately 7,000 km, the car suffered a "hardening of the suspension and breakage at the splines of the reaction lever on the cylinder" p. 95.

The dismantling: six findings

1. The rear right suspension sphere is full of Lockheed on both sides of the membrane; the membrane (Michelin manufacture) is "punctured (star-shaped puncture)" within the valve support circle, probably due to a foreign body — a torn damping valve washer of which a piece was missing p. 95.
2. On the shock absorber, a 5/100 shim was torn (piece missing) and the damping valve was jammed on the shaft, which had become conical p. 95.
3. The reaction lever on the cylinder broke at the splines "due to a lack of elasticity"; the splined shaft twisted p. 95.
4. The connecting rod (in Ol-G+T2) between the lever and piston "behaved well", with a slight pitting point on the piston side, but showed oxidation "from the lower cover to the upper end, including the joint" p. 95-96.
5. The ball and needle bearings (D side) were "in good condition, well greased" p. 96.
6. The triangulation tie-rod attachments were in good condition, but insufficient adjustment had offset the rear wheels to the right p. 96.

The document bears a dated receipt stamp and three handwritten signatures not identified with certainty p. 95.

Context

The acronym PVL designated, at Citroën, the prototype vehicles used for road tests before the development of the future DS, whose hydropneumatic suspension was the major innovation launched in 1955. These endurance tests in real conditions, over tens of thousands of kilometres, were part of the long process of making the system designed by Paul Magès in the 1940s-1950s reliable.

Archivist's perspective

This report concretely illustrates the engineering difficulties encountered before the industrial success of the hydropneumatic suspension: material failures (punctured Michelin membrane, torn shims, oxidation), design problems (lack of lever elasticity) and adjustment issues (rear wheel offset) combine p. 95-96.

It seems that this document belongs to a vast corpus of test reports intended for Magès to guide the successive corrections of the system, in continuity with the theoretical studies conducted from the 1943-1944 years, as evidenced by the folder "Theoretical study – hydropneumatic suspension 1943/44". It could also be linked to the 1945 manufacturing schedules for the suspension, which organised the production of the parts tested here.