Handwritten note of 24 June 1959 – "Capacity per axle" case: calculation of pressures in a turn

In this document

The schematic diagram

The page presents a symmetrical technical diagram: a central compressor ("Comp.", noted 10 kg/cm²) connected by two conduits to a left assembly (G) and a right assembly (D), each composed of several 1 dm³ capacities marked ①/② and A, with sections of "100 cm²" and pressures of "5 kg/cm²" indicated on the lower rectangles p. 10.

Calculation in a straight line

In a straight line, Magès sets the equilibrium values: "PG = 500 kg" and "Pd = 500 kg", for a total of "1000" p. 10.

Calculation in a turn

In a turn, he considers an asymmetrical distribution: "PG becomes 750" and "Pd... 250", the total remaining "1000" p. 10.

To restore equilibrium, while keeping the reservoir at a constant 10 kg, he calculates that it is necessary, on the left side, to go from 10 to "2.5" and on the right side from "10" to "7.5": thus "on the left it is necessary to lose 2.5 at atmos. pressure (via jet 2)" and "on the right it is necessary to add 2.5 of air at atmos. pressure (via 1)" p. 10.

He then notes that if the compressor does not supply, there is a lack of "0.250 of air at 10 kg", which produces a calculated lowering — "2.50 cm³ / 200 cm² = 1.25 cm" — in the median plane p. 10.

He concludes that the speed of the "restoration" in a turn depends on the flow rate of the jets (2 on the left, 1 on the right for a right turn), because equilibrium can only be achieved, without large piston displacement, "by pressure variation via intake (or exhaust) in the lower chambers" p. 10.

The page bears the handwritten date in red "24/6/59" and a second date in the margin, "29/6" p. 10.

Context

This note is part of, as we know from the history of Citroën, the research conducted at Citroën on the hydropneumatic suspension of the DS and its variants, at a time when engineering was exploring different capacity distribution architectures (per axle or per side) to manage cornering behavior.

The term "capacity per axle" refers to a design choice opposed to "capacity per side", two options then compared in the pneumatic/hydropneumatic suspension studies of the period — a debate found in several contemporary notes in this file.

Archivist's perspective

This sheet illustrates, in a very concrete way, Paul Magès's working method: calculated pressure figures, supported by a hand-drawn diagram, to anticipate the dynamic behavior of a suspension in a turn rather than settling for a qualitative intuition.

The double date — "24/6/59" in red and "29/6" in the margin — probably suggests a resumption or a re-reading of the note a few days later, which is consistent with the existence of a very similar note dated the same day, Effects of a capacity per side or per axle, on gallop and roll, and another from 29 June on the same subject, capacity per side vs capacity per axle.

This "capacity per axle" case thus seems to be a piece of a series of systematic comparisons between architectures, conducted by Magès a few days apart in June 1959, probably in connection with the broader work on pneumatic suspension mentioned in the "M. Bongrand" file.