Hydropneumatic suspension plans with differential interaction (17 February 1944)

In this document

Dating and folder

Pages 9 and 10 bear the handwritten date "17-02-44" p. 9-10. Page 10 serves as a cover/folder and indicates the title "Hydropneumatic suspension plan with differential interaction and automatic leveling" as well as the mention "Detail plan" p. 10.

The general diagram (p. 11)

A large unfolded technical plan details the complete architecture of the system: a RESERVOIR, an ACCUMULATOR, a PUMP, a PRESSURE GAUGE, an AIR BELL, a "LOCKING AND BALANCING BLOCK", a "DIFFERENTIAL INTER-ACTION BOX [housing?]", an ELECTRO-VALVE, a "RELAY-DILAT[…]", a SUSPENSION CYLINDER connected to the REAR WHEEL, and a "HEIGHT CORRECTOR" p. 11. The title block at the bottom right includes the full title "HYDROPNEUMATIC SUSPENSION WITH DIFFERENTIAL INTER-ACTION AND AUTOMATIC LEVELING" with a scale mention of "Principle" p. 11.

Technical cross-sections (p. 12)

A crumpled tracing paper sheet presents several cross-sectional views, designated "section A-A" and "section B-B", accompanied by handwritten text mentioning a "c/action with piston for [releasing] air […] from the liquid" p. 12 — foreshadowing the solution detailed on page 13.

Solution with air/liquid separation piston (p. 13)

This plan, titled "Solution with Air & liquid separation piston" p. 13, details in cross-sections ("Section A A", "Section C.C", "Section A.A") a hydraulic block marked by the letters A, A', B, B', with two "bleed screws" p. 13. A handwritten paragraph discusses the inflation conditions of B and A "provided that one can count on sufficient sealing", and specifies that if this is insufficient, "the difference in K value" will have to be compensated "by difference in capacity" (p. 13, passages partially uncertain).

A block of numerical references ("6.56 S.147", "Started on 12.5", etc.) and a handwritten signature accompanied by an uncertain date "14.12.[…]" appear at the bottom of page 13, but remain largely illegible.

Context

The term "hydropneumatic suspension with differential interaction" refers to the research conducted by Paul Magès at Citroën during the Second World War, which would lead after the war to the hydropneumatic system equipping the Citroën DS (1955) and then other models. The notion of "automatic leveling" refers to the principle, central to this invention, of maintaining the vehicle's height constant regardless of the load — a characteristic that would become emblematic of the DS.

The operation via "air bell" and "locking and balancing block" falls under the founding principles of hydropneumatics: a compressed gas (air, then nitrogen) separates the suspension energy from the liquid circuit, a separation that would later be ensured industrially by a spherical membrane — which the plan on page 13 seems precisely to be trying to solve via a "separation piston".

Archivist's perspective

This bundle of plans, dated 17 February 1944, testifies to a still experimental design stage: the general diagram p. 11 sets out the complete architecture of the system, while pages 12 and 13 focus on a specific technical point — the physical separation between air and liquid within the circuit — a problem that Magès seems to be trying to solve through several piston variants.

The handwritten paragraph on page 13, which discusses the sealing conditions necessary for the proper inflation of the system, suggests that this was a technical bottleneck actively worked on during this period, probably in connection with the tests and reflections recorded in the List of problems under study as of 22 February 1944, a nearly contemporary document.

This plan is part of the larger corpus of the "41.59" folder, whose Summary allows this piece to be situated among all the hydropneumatic suspension studies conducted by Magès during the war.