Manuscript study of the "garage position" of the hydraulic gear shift (29.9.52)

In this document

This manuscript sheet, dated "29.9.52" and "6.10." and referenced "II", studies the garage position of a hydraulic gear shift project, with the mention "Po=0" and "idle engine at 1200 [uncertain]" p. 3.

The diagram

The central sketch shows a set of parts connected by conduits: a circular device marked "PM" with the markers "3en" and "2en" (probably 3rd and 2nd gear), an area marked "8° variable pressure of the 2° device" connected to a "reservoir", as well as a "Repartiteur" (distributor) and an "Accu" (accumulator) connected to "wheel / idle engine" p. 3.

Operating notes

The text mentions the switching on to "PM", which would go "out of circuit once pressure is obtained" p. 3. It also mentions a pressure which, once reached, would close "the PV return" "for [uncertain] time [uncertain] (slow) while waiting" for the gear to "receive" the "full pressure" p. 3.

The author notes that "the V pump should be less strong" once "the gear is shifted", and that "the M pump" should be "limited to a pressure slightly higher than that of the clutch" p. 3.

A final remark concerns the operation of the pumps: for better operation, they should be "consecutive" — one under pressure while a gear is engaged, the other when the engine drops "below 1000 r[pm]" p. 3.

A separate note in red indicates "2.V.52"; above it, in black, a sentence specifies: "If Po=0 the gears are shifted without [uncertain] synchronism[uncertain]" p. 3.

Context

This document belongs to the exploratory phase (1952) of the hydraulic gear shift project that Paul Magès was developing at the time at Citroën, in line with the research that would lead to the hydropneumatic suspension of the DS.

The concepts of pump, accumulator ("Accu") and pressure distributor mentioned here recall the general architecture of Citroën hydraulic circuits of the time, without this precise link being established by the document itself.

Archivist's perspective

This sheet seems to be a variant or an elaboration of an earlier sketch: the reference "II" and the repetition of the "Po=0" principle suggest a serial numbering of successive studies on this same mechanism, of which a first milestone can be found in the First sketch of a hydraulic gear shift.

The technical vocabulary used — "PV", "PM", "Accu", "Repartiteur" — overlaps with that of other sheets in the same file, notably the Sketch of hydraulic circuit with pipe markers, which suggests continuous development work over a few days (29 September to 6 October 1952).

The double dating and the red note "2.V.52" remain difficult to interpret with certainty; they could mark a later review or filing, but this is not specified in the document.