Magès note to Mr. Bongeard: suspension calculations and rubber bump stop (2.7.59)

In this document

This handwritten note by Paul Magès is addressed to Mr. Bongeard and accompanies the sending of three technical drawings: two drawings referenced E4019035 and E4019036, as well as a drawing A4551a p. 4.

Calculation of suspension pistons

Magès explains that the first two drawings "provide calculation elements to establish the suspension", while the third "gives the characteristic of a rubber bump stop" usable either internally or externally p. 4.

The sizing of the piston surfaces was established based on the maximum load and an operating pressure of 8 kg/cm² (relative pressure). The diameters obtained are as follows:

By finally adopting a diameter of 116 mm at the front, Magès notes that "equilibrium is obtained with a pressure on the other face of 8-6.2=1.8" p. 4.

Flexibility and comfort

Magès then addresses the volume of "R" capacities to be provided for each wheel, estimated "to obtain the flexibility that we deem necessary for comfort" p. 4. He specifies that this calculation is made "as if the capacities were independent", the actual result differing "due to their interconnection (in the right direction)" p. 4.

He mentions a lack of flexibility in the rebound movements "which seems to be particularly lacking on the 4CV" p. 4, and recommends a relatively large R1 capacity to remedy this.

Finally, he suggests that the cylinders should only have the length necessary for the requested travel, with all the air volume useful for flexibility being placed outside — including for R1 — "to make maximum use of the possibility of air damping" p. 4. He also wishes for the loads and damping between the cylinder and R/R1 capacities to be "easily changed" p. 4. The note ends with a reference to a subsequent oral discussion.

Context

Paul Magès is, in the history of Citroën, the designer of the hydropneumatic suspension, introduced on the DS in 1955. The name Bongeard (sometimes spelled Bougeard or Bongrand in other documents in the collection) appears associated with work on a competing or parallel air suspension, mentioned in several exchanges from the same period.

The 4CV mentioned in the note refers to the small popular post-war Renault, here taken as an example of a vehicle whose rebound movements would lack suppleness — a technical point of comparison external to the central subject of hydropneumatic capacities.

Archivist's perspective

This working note, dated 2 July 1959, is likely part of a larger file devoted to the comparison between air suspension and hydropneumatic suspension, as suggested by the cover page "Mr. Bongrand — Air suspension, 59-61".

It testifies to Magès' constant concern to optimise the balance between pressure, piston diameter and air volume for comfort, a preoccupation found in other handwritten notes from the same week, such as that of 24 June 1959 on the effects of one capacity per side or per axle.

The practical tone and the announcement of a discussion "in person" suggest that this is a piece of routine technical correspondence rather than a definitive summary document — a work milestone among others in the development of the pneumatic suspension systems of the time.