Paul Magès' notes on the DS clutch and gear control (28 March 1961)

In this document

This handwritten note by Paul Magès, titled "AMELIORATIONS DS" — "EMBRAYAGE & COMMANDE DES VITESSES" (p. 12, title repeated p. 14), bears an inscription in red ink "3 61" suggesting March 1961 p. 12.

The accelerated idle

The "accelerated idle", integrated into the carburettor fitted with the Damper engine, provides several advantages according to Magès: less effort on the brake pedal to drop the speed at a "red light" (approximately 3 Kg/cm²), more practical adjustment, less reaction on the throttle shaft, and the possibility of reducing the accelerator spring to prepare for a progressive accelerator p. 12.

The declutching corrector

A piston housed in the centrifugal control device of the automatic clutch receives, during braking, a pressure allowing the declutching curve to be shifted by 10 Kg/cm². Magès notes that the trigger threshold should be lowered to approximately 3 Kg/cm², and proposes as a solution using the 6.35 piston of the accelerated idle as a high-pressure distribution spool p. 12. He specifies that the accelerated idle should in any case be rethought for the "N engine", because it interferes with the gear change block p. 12.

Observations on the carburettor

Magès reports that the hydraulic settings do not evolve over time, but that the engine idle does evolve — not because of the engine, but because of the carburettor setting. With the Solex carburettor, he states that "we are absolutely certain of it today", the evolution is zero (reference to the "Gaudin" case, taxi). The bronze bushings for the throttle shaft do not seem to have solved the problem after 4000 km p. 13.

The re-clutching corrector

A "new principle" is under study: as soon as the re-clutching signal is received, the pressure drops suddenly to a "licking" pressure independent of the engine speed, set once and for all; then progressive reduction to zero, slower "foot lifted" to avoid "engine braking jolt", and also relatively slow at "half-throttle" p. 13.

Context

The centrifugal automatic clutch and the semi-automatic gearbox (BVH) of the DS relied on the high-pressure hydraulic circuit developed by Citroën. The Solex carburettor, cited in the note, commonly equipped Citroën engines of the time. These contextual elements are general knowledge about the DS, not from the document itself.

Archivist's perspective

This document illustrates Magès' meticulous work on the links between braking, acceleration and automatic clutch, the heart of his hydraulic engineering. Field observations (the "Gaudin" case) show an engineer's method attentive to real-world usage feedback.

This note is likely a continuation of the reflections presented during the BBC Conference of November-December 1960, and finds a later echo in the Summary of the BBC session of 22 February 1962, which also deals with transmission and gearbox.