Steering return servo-control: mechanical principle and variable flow regulator

In this document

This page (numbered "8" at the top, p. 13 of the scan) deals with steering return servo-control, presented as the combination of two functions already seen previously: hardening and assistance, the former controlling the latter p. 13.

Mechanical principle

The text describes the sequence that occurs when the driver releases the steering wheel after a turn: piston F exerts torque on cam H, causing it to rotate; pinion P.5, integral with the cam, drives the control shaft P.1; the latter, via plate P.4, tilts the distributor slide valve T.1, which moves the steering rack p. 13.

The movement stops when roller G returns to the hollow of cam H, causing the "cancellation of torque": the steering then returns to the "straight line" position p. 13.

A note specifies that the regulator pressure only acts on piston F through a variable flow regulator, whose role is to brake the return of the steering to the straight-line position p. 13.

The variable flow regulator

The document details its composition: a body in which a piston (F) slides, a sleeve A pierced with a calibrated hole (I) and capable of receiving small orifices (D), a spring (B) acting on the sleeve, and a valve with its own spring (C) p. 13.

The operation in the neutral position (straight line) is described: the regulator pressure then prevails in the three chambers 1, 2 and 3; spring B, under tension, keeps sleeve A closed over orifices D, making the flow possible through the calibrated hole I zero p. 13.

Three captioned diagrams accompany the text: the complete mechanism (cam, pinion, slide valve, rack), the variable flow regulator, and a simplified sketch of cam H with its roller G p. 13.

Context

This mechanism corresponds, in the history of Citroën, to the power steering with automatic return system (the DIRAVI, "DIRection Asservie à Rappel automatique et Incorporé" [Servo-assisted steering with incorporated automatic return]) developed under the impetus of Paul Magès and introduced on the DS then generalized on other models (SM, CX...).

This system remained famous for its ability to spontaneously return the steering wheel to the straight-ahead position, without driver intervention — a feature that strongly distinguished hydraulic Citroëns from their competitors. This general knowledge is not, however, explicitly stated as such in the present page; it only allows the technical vocabulary of the document to be placed in context.

Archivist's perspective

This page probably belongs to internal educational material, in the vein of the "Hydraulic Expert Notebooks" that Citroën circulated to train its technicians in its in-house inventions. The numbering "8" at the top of the page suggests that it is a leaflet extracted from a longer notebook, whose "hardening" and "assistance" functions would have been covered in previous pages not transmitted here.

The precision of the diagrams and the parts vocabulary (P.1, P.4, P.5, T.1...) evokes a document intended for technicians rather than the general public — probably a piece of the same documentary vein as the Hydraulic Quiz No. 5, which specifically concerns the DIRAVI and the pressure regulator. To understand the institutional framework of this type of material, one can also refer to the biographical notice of Paul Magès, which traces the genesis of these hydraulic innovations.