Hydraulic suspension test report of 12 May 1949 (Mr. Magès)

In this document

This report signed by Mr. Magès, dated 12 May 1949, recounts a series of comparative road tests of hydraulic suspension, conducted with Messrs. Boulanger, Lefebvre, Duclos and Cadiou p. 73.

The reference setting (A)

The day's tests are compared to the setting used during a Paris-Clermont-Aubusson trip on 5 and 6 May. This "A" setting included inflation of the spheres to 60 kg/cm² (front and rear), damping via cones (compression 90°, extension 6° at the front and 3° at the rear) and a roll bar set at the 4th hole (Ø=16.8) p. 73.

The impressions noted for this A setting: "lack of fluidity (bottoming shocks, transverse movements and shocks)" compared to the traction (TPV), a pumping or galloping movement judged "almost perfect", and cornering stability at Aubusson "excellent - no concerns" p. 73.

The day's tests (B, C, D)

Three tests are conducted on the Paris - Les Bruyères - Petit-Clamart - Les Bruyères route, by varying the shock absorber spring and especially the roll bar setting:

Mr. Duclos notes for test D "no shocks - lower windshield displacement, impression of unstable balance" p. 74.

The final conclusion summarizes: test A (Clermont) gives "excellent pumping and galloping" with shocks "a little too perceptible"; test B makes the shocks forgotten; lateral displacements remain "to be eliminated" p. 74.

Two tests are then proposed: a stronger roll recall than in test C, and a roll recall distributed between the front and the rear p. 74.

Context

These tests are part of the work carried out by Citroën during the years preceding the presentation of the DS in 1955, on what would become the hydropneumatic suspension — a development whose initial plans date back to 17 February 1944 (Hydropneumatic suspension plans with differential interaction (17 February 1944)) and whose first tests on 2 CV had taken place in May-July 1946 (Notebook of the first 2 CV hydropneumatic suspension tests (May-July 1946)). This May 1949 report is therefore situated between these two milestones and the test of the 15-Six H of April 1954 (Road test of the 15 Six H (ELV 412) by Paul Magès, 3-5 April 1954). Pierre Boulanger was then leading Citroën, while Lefebvre was technical manager — their presence during these road tests illustrates the importance given by management to these developments. Nothing in the document, however, specifies the test vehicle used.

Archivist's perspective

This report offers a rare snapshot of the empirical work of Magès and his team: the method by successive comparisons, setting by setting, on the same route, illustrates a rigorous and iterative engineering approach p. 73-74.

It seems that the difficulties encountered with the roll bar — arbitration between fluidity, galloping and cornering stability — constitute a central problem of the development, recurring in the works of the period, as evidenced by the Folder "Theoretical study – hydropneumatic suspension 1943/44". This document can also be compared with the Manufacturing schedules 1945 to situate the progress of the project in time.