Note no. 669 by Paul Magès on the Direction à Rappel Asservi (16 February 1970)

In this document

History and technical context (p. 1)

The note recalls that the DS was "from 1955 the first car equipped as standard with power steering" p. 1, made necessary by the weight on the front and the road-holding of the hydropneumatic suspension. A "compromise" had then been sought between assistance for garage manoeuvres and high-speed stability p. 1, at the cost of an adaptation period for drivers — Magès even mentions the initial tendency to "turn at the street corner" p. 1. A similar problem had arisen for the power braking of the DS p. 1.

The "S" vehicle and the steering ratio (p. 1-2)

In 1970, the "S" vehicle (more powerful than the DS 21) required rigid tyres and a more rigid steering linkage, which increases the change in heading for the same angle at the steering wheel p. 1. Magès explains that the understeer character desired for the "Traction Avant" requires a lot of steering in corners p. 2, and that a "very direct and well-assisted" steering is necessary to exploit the possibilities of the vehicle in corners as well as in obstacle avoidance p. 2.

American tests (p. 3)

"Scientifically conducted experiments" in the U.S.A. are cited: a test with a device causing a steering deviation without the driver's knowledge and recording the trajectory, conducted with "about forty male or female drivers", showed a faster and more precise return to the trajectory with low-ratio steering p. 3.

The Direction à Rappel Asservi - DRA (p. 3-5)

After several years of study, Citroën arrived at the Direction à Rappel Asservi (DRA) p. 3, applied to the "S". It requires "practically no effort" in garage manoeuvres, returns to the straight line on its own p. 3, locks the wheels at a defined angle independently of disturbances (tyre burst, puddle, asymmetric braking) p. 3, and offers an energetic return that increases with speed p. 3-4, particularly useful on "snow - ice" p. 4.

Choice of steering ratio and reactions (p. 5-6)

The chosen steering ratio is 9.4 (at the centre), compared to 14.7 on the power-assisted DS p. 5. Initial tests show immediate adaptation in road driving, with difficulty persisting mainly in garage manoeuvres p. 5. The document concludes with a comparison with American cars, deemed unsuitable for direct steering due to their weight and inertia p. 6. The note is signed "P. MAGES" and dated "16 February 1970" p. 6.

Context

The "S" vehicle mentioned corresponds, in the history of Citroën, to the project that would become the SM, launched in 1970 in association with Maserati — knowledge external to the document, as it never names the SM explicitly. The DRA would indeed be fitted as standard, a world first for power steering with synthetic return. The comparison with "American cars" is part of the technical debate of the 1960s-1970s regarding soft suspensions and large saloons, then subject to increasing speed limits in the United States.

Archivist's perspective

This internal note, referenced "no. 669", seems to constitute a summary document intended to explain and defend, internally or to technical interlocutors, Magès's choices regarding the DRA at the time of its introduction — probably in preparation for or accompanying the launch of the "S" vehicle p. 1-6.

The pedagogical tone, the anticipated objections ("One could object that...", p. 2) and the historical reminder since the 1955 DS make it a key text for understanding the continuity of Magès's thinking on power steering, from the DS to the SM. It usefully complements the archives concerning the hydropneumatic suspension, of which the DRA shares the same philosophy of servo-assisted steering.