Diravi: Paul Magès' power-assisted steering (Wikipedia excerpt)

In this document

This is a printout of a Wikipedia page dedicated to the Diravi power steering, devised by engineer Paul Magès, presented here as "already the developer of the DS hydropneumatic suspension" p. 1.

Constant, not variable, assistance

The text corrects a common misconception: contrary to what is "often presented", the Diravi's assistance is not variable but constant. In reality, it is the straight-line return force that is speed-sensitive, which gives the deceptive impression of decreasing assistance during small steering angles p. 1.

The technical principle of speed-sensitive return

the document describes a precise mechanism: the steering column carries a "heart-shaped" cam, on which a roller exerts radial pressure. The roller sits in the hollow of the cam when the wheels are in the straight-ahead position. The pressure is regulated by a centrifugal device located on a gearbox shaft p. 1.

Irreversibility and benefits

The Diravi is described as irreversible: movement is transmitted only from the steering wheel to the wheels, never the other way around. The driver therefore only has to manage the steering, with the system returning the wheels to the straight-ahead position on its own. The document sees this as a double gain, in comfort (non-transmission of shocks) and safety (absence of steering wheel movement due to road surface irregularities) p. 1.

SM/CX comparison

A steering ratio of 2.5 turns lock-to-lock is indicated for the CX, compared to 2 turns on the SM p. 1.

The page also includes a partial photograph of a car dashboard, as well as typical Wikipedia interface elements ("edit" links, external link icon) p. 1.

Context

To provide context: the DS (1955) and the SM (1970) then the CX (1974) are iconic Citroën models from the era when the brand's hydraulic engineering, led in particular by Paul Magès, distinguished itself through innovations in comfort and road holding. The DS hydropneumatic suspension, whose plans from 17 February 1944 (Differential interaction hydropneumatic suspension plans) and initial tests on the 2 CV (May-July 1946, initial test notebook) precede the presentation of the DS on 6 October 1955, is a historical milestone in the automotive industry; the Diravi constitutes a logical extension applied to steering, generalizing the principle of hydraulic assistance controlled by a pressurized fluid (LHM at Citroën). Magès, who joined Citroën in August 1925 and remained for 49 years until his retirement in September 1974 (draft letter to Mr. Sarre; photographs of retirement), thus accompanied this entire technical lineage, from the DS to the CX. These elements are partly part of general automotive culture and partly facts established by the collection; they do not come from the document itself.

Archivist's perspective

This document is not an original piece from Magès' personal archives, but a printout of an online encyclopaedic article — likely kept in the collection for its explanatory value, in order to enlighten the general public on a complex technical system attributed to the engineer.

It illustrates well how posterity summarizes, sometimes in a didactic and corrective manner ("in reality, the assistance is constant"), one of Magès' lesser-known contributions, the Diravi, alongside his most famous invention, the hydropneumatic suspension. It could usefully be compared with original technical archives on the Diravi, if they exist in the collection, to compare the encyclopaedic narrative with the design documents themselves.