1946 technical note on the automatic height adjustment and stabilisation device

In this document

Presentation of the problem and general principle

The memorandum opens with an observation: many devices have already attempted to automatically adjust vehicle height and counteract tilting in corners, but "all these solutions have encountered practical implementation difficulties" p. 1. Magès specifies that the originality of his project "resides only in the combination of all its elements, known for a long time, to make a coherent 'whole'" p. 1.

The described system comprises five elements: a suspension with a reaction point displaceable by a hydraulic piston, a control device connected to the four wheels, a system of slide valves for slow height correction, a second system for instantaneous transverse correction, and a hydraulic power unit with pump and reservoir p. 1-2.

The control device (fig. 1)

Connected by four cables marked AVG, ARG, AVD, ARD to the four wheels, this mechanism of springs and levers (1 to 15) continuously detects the average front and rear height, the transverse inclination, and the lack of parallelism of the chassis p. 2-4. A Dash-pot (damper, reference 13) filters rapid movements to transmit only slow attitude variations p. 3.

Typical suspensions (fig. 2 and 3)

Two examples are given: a torsion bar suspension whose reaction point is a piston 16 in a cylinder 17 fed by piping 18 p. 4, and a link suspension 23 with piston 24, cylinder 25, and compressed gas capacity 26, where "it is the load on the wheel that automatically determines the equilibrium pressure" p. 4-5.

Hydraulic distribution (fig. 4 and 5)

The pump P and the reservoir R feed two blocks of slide valves: the first (fig. 4) with the slide valves HAV, HAR and IT regulates the front/rear height and the inclination p. 5-6; the second (fig. 5), with IT', SG and SD, corrects the transverse balance while avoiding any parasitic longitudinal attitude variation p. 6-7.

The final summary insists: the system "cannot have inter-communication between the suspensions of the different wheels" outside of correction phases, and functions "without modification of flexibility" p. 7. The document is dated 18/11/46 at the end of the text p. 7, with the handwritten date 16.10.46 on page 1.

Context

This technical memorandum, annotated "16.10.46" and "1.003.175" (probable reference to a patent filing), is part of the research conducted at Citroën after the war on hydraulic suspension, while Paul Magès, who joined Citroën in August 1925, had been working in the design office since the early 1940s (draft of a letter from Paul Magès to Mr. Sarre). It follows the first plans for hydropneumatic suspension with differential interaction dated 17 February 1944 (Hydropneumatic suspension plans with differential interaction), and shortly precedes the first tests on the 2 CV conducted in May-July 1946 (Notebook of the first tests of the 2 CV with hydropneumatic suspension).

We know, from the collection itself, that this work would lead about ten years later to the hydropneumatic suspension, tested on the 15-Six in April 1954 (15-Six H test) then presented on the DS on 6 October 1955, which would precisely combine height correction and comfort via gas spheres. The principle of the compressed gas capacity described here (fig. 3) prefigures this device, but nothing in the document itself refers to the DS, which did not yet exist in 1946.

Archivist's perspective

This document is one of the very first descriptive memoranda written by Paul Magès to formalise, with a view to a patent filing, the complete principle of attitude correction that he would then develop for nearly a decade at Citroën, until its presentation on the DS in 1955.

It seems that we have here a pivotal stage: the coexistence, in the same text, of the classic mechanical solution (torsion bar, p. 4) and the compressed gas solution p. 4-5 which would become the chosen path, suggests that the technical choice had not yet been finalised at that date.

To understand this memorandum in its visual detail, one should usefully refer to the Plates of figures 1 to 5 of the automatic height adjustment device, which directly accompany this technical note.