Magès calculation note: P55 suspension, leaf spring and 6 spheres (4 March 1958)

In this document

This handwritten sheet, dated 4 March 1958 and signed "P. Magès", contains calculations for the suspension of the P55 project p. 6.

Principle of the studied suspension

The title indicates a hybrid suspension: "Leaf spring supporting 1/2 weight + HydroPneumatic suspension" with 6 spheres of 750 cm³ p. 6.

Inflation and pressure data

Magès notes the following values for the 6 spheres:

The amount of oil required to move from the "unladen" to "laden" position is calculated at 3.440 p. 6.

Choice of pump

Magès reasons based on a 7-piston pump (displacement 2.8 cm³). He calculates that 1250 revolutions would be needed to provide the required volume, i.e., 30 seconds at 2500 rpm — a duration underlined in pencil in the document p. 6.

He deduces that a pump linked directly to the engine speed should be ruled out, as this would impose excessive engine acceleration p. 6.

He considers two alternative solutions:

• an electrically controlled pump for rapid height adjustment, supplemented by a booster pump during travel p. 6;
• a two-speed mechanically controlled pump, with a manually engageable high-speed gear, automatic disengagement upon releasing the handbrake, and a clutch he considers "advantageously magnetic", controlled by a pressure-sensitive pressure switch p. 6.

Context

The P55 project corresponds, in the internal Citroën nomenclature of the time, to studies of vehicles derived from the DS/ID range, whose hydropneumatic suspension — invented by Paul Magès — already equipped the DS 19 marketed since 1955.

The hybridization mentioned here (leaf spring + hydropneumatic spheres) recalls the solutions used on other Citroën models of the time for the rear axle, where pneumatic comfort was sometimes combined with more conventional mechanical elements, particularly for reasons of cost or payload.

Archivist's perspective

This sheet illustrates the daily dimensioning work carried out by Magès: this is not the design of the hydropneumatic principle itself, already proven on the DS, but a very concrete engineering problem — how to supply oil, quickly enough, to a 6-sphere system without excessively straining the engine.

The reflection on the pump (electric vs. two-speed mechanical, magnetic clutch, pressure switch) shows Magès's concern to anticipate real-world usage constraints (rapid ascent, handbrake, road). It seems that this document belongs to a study phase that was still open, probably prior to a final industrial choice.

This note can be compared to other items in the same collection dealing with suspension spheres, such as the pressure survey of pneumatic suspension blocks (P 1662), or the handwritten study sheet on mass-spring curves, which document complementary aspects of the same type of calculations.