Front-Rear Interaction Suspension Project (technical note, 13 January 1944)

In this document

The problem posed

The note opens with an observation: an interaction between the front and rear suspensions "considerably improves comfort" p. 1. The author reviews previously proposed solutions—variable-length levers, or front-rear linkage via a "gallop spring"—and highlights their limitations, particularly for vehicles with "large variations in load distribution" p. 1.

The proposed system

The described solution uses two elastic elements placed in parallel, each acting on the front wheel and the rear wheel via levers of different lengths: "the lever arm on the front of one of the springs is larger than the lever arm on the rear," and vice versa for the other spring. The text describes this principle as a "differential action system" p. 1.

The document specifies that this system "always, automatically, finds a position of equilibrium," regardless of the load distribution, provided that the ratio of front/rear loads remains within limits set by the dimensions of the levers and the characteristics of springs R and R' p. 2.

Illustrated variants

Four figures accompany the note p. 3:

• Fig. 1: mechanical principle diagram, coil springs, points A, B, R, R', O, O' (p. 1, p. 3).
• Fig. 2: "hydraulic suspension based on the same principle of differential action," air or compressed gas as the elastic element p. 1-2.
• Fig. 3: variant with differential pistons (points P, A, P', A') p. 1-2.
• Fig. 4: centralized differential pistons p. 2.

The final Summary reformulates the principle: two or more elastic elements per side, acting "with the same force" on the two opposite wheels, but with a different moment, stronger at the front for one, at the rear for the other p. 2.

Context

This note, dated 13 January 1944, is part of the suspension research conducted at Citroën in the years preceding the launch of the DS (1955), whose hydropneumatic suspension—combining liquid and compressed gas under pressure—would become a major technical signature of the brand.

The archive allows us to clarify this connection: a little over a month after this note, on 17 February 1944, Paul Magès drew up his own plans for a hydropneumatic suspension with differential interaction, having joined the Citroën design office shortly before thanks to his work on the braking limiter for the TUB van (1939-1940). The front-rear interaction principle described here, particularly in its hydraulic piston form (Fig. 2 to 4), is thus part of the same sequence of reflection that would lead, via the first tests on the 2 CV in 1946, to the hydropneumatic suspension of the DS presented in 1955.

Archivist's perspective

This text takes the form of a structured invention note (statement of the problem, technical description, final summary), probably intended to serve as a basis for a patent filing or internal consultation—although the document does not explicitly state this.

It seems that this piece marks a stage of reflection prior to the fully developed hydropneumatic solutions: the transition from the mechanical lever system (Fig. 1) to the hydraulic variants with differential pistons (Fig. 2-4) illustrates, within the document itself, a logical progression towards architectures closer to what would become characteristic of Citroën suspensions.

The date of 13 January 1944 p. 1 places this project in the middle of the Occupation period, which could explain the still theoretical and exploratory nature of the note, although no element of the document allows this to be confirmed.