1961 patent addendum: anti-roll device for motor vehicles

In this document

This typewritten text constitutes an addendum to the main patent concerning an anti-roll device for motor vehicles. Its objective is clearly stated in the introduction: "to replace the pump 28 and the system of valves and pistons described in the 1st addendum, in all cases of use of a hydraulic or pneumatic power steering system for a vehicle" p. 1. The text specifies that this device "is applicable regardless of the design of the cylinder" p. 1.

Described operation

The mechanism relies on a valve system 42, mounted on the pipes 43 and 43 bis, which generates a pressure difference P1/P2 as soon as there is liquid flow in the steering cylinder 44, "either in one direction or the other" p. 1. This pressure difference, calibrated by "the load of the valve springs 47 and 48", moves the pistons 49 and 50, then the piston 51, the stroke of which regulates the volume delivered to the piston 19 of the distributor 13 p. 1.

The text also describes a special case: if the steering wheel is immobilized while cornering, "the pressures P1 and P2 balance out via the nozzle 54", and the piston 51 returns to the middle position thanks to the springs 55 and 56 p. 1. Two variants of this return to the middle position are presented, corresponding to figures 1 and 2: balance of the springs 55/56 in the first case, stop of the spring cups 57/58 on the faces F1/F2 in the second p. 1.

Page 2 contains the corresponding technical diagram, with all the cited references (13, 19, 42 to 58, P1/P2, F1/F2, 43 bis), signed "M. Magès" and bearing the handwritten note "MODIF." as well as the inscription "Essai 43204" p. 2.

Context

This document is part of the development of the Citroën hydropneumatic suspension, for which power steering and roll management in corners were major technical challenges for the future DS. Patent addenda, common in the industrial practice of the time, made it possible to protect successive improvements to a main invention without re-filing an entire patent — a practice consistent with Paul Magès' continuous work on these systems during the 1950s-1960s.

Archivist's perspective

This document clearly illustrates Magès' working method: a rigorous technical description, supported by a hand-annotated diagram, with a part numbering system that seems to take up and extend that of an earlier "1st addendum" p. 1 — the latter not being present in this archive but explicitly mentioned as a reference.

The handwritten note "MODIF." and the "Essai 43204" p. 2 suggest that this diagram was probably subject to an experimental adjustment after a bench test, a sign of an iterative process typical of the development of hydraulic devices at Citroën.

The interest of this piece lies in its pivotal position: it documents a deliberate simplification of the anti-roll system (replacement of a pump and a set of valves by a differential piston device), testifying to a constant search for mechanical refinement characteristic of Magès' inventions.