Technical drawing of the DS 334-26 piston — hydraulic control of the selector forks (6 October 1956)

In this document

This technical drawing concerns the DS 334-26 piston, designated as "2nd, 3rd and 4th gear piston", a part of the "Hydraulic control of the selector fork shafts" p. 20 — that is, the hydraulic component responsible for moving the DS gearbox selector forks.

The technical drawing

The plate shows a cylindrical part in longitudinal section, with its main dimensions: length 34.5 ±1 and 41.2 -0/0.05, several diameters (Ø1 to Ø4) with tight tolerances. Finishing indications specify: "Centre and nipple prohibited", "Flat allowed on Ø=2 max", "Convex 0.2 to 0.4" p. 20. A detail enlarged to scale 5 (Ech 5) shows the end of the part, with a chamfered angle at 30°+5°/0, a radius r=0.5 max and a dimension 0.6 +0.7/0 p. 20.

The variants table

The drawing groups two piston references sharing the same plate:

The signature block

The material used is C4 steel, without coating p. 20. The signature block mentions the draughtsman Perrin, dated 6-10-56, with verification by Bastien and industrial inspection by Guyétant; on the laboratory side (BEA), the names Pompon, Caneau and Cadiou appear, without date or signature provided p. 20. Two handwritten modifications are noted: "m1 redone 27364" and "m2 25.27669" p. 20. The whole is protected by the printed mention "Société Anonyme André Citroën — Reproduction prohibited" p. 20.

Context

The DS, introduced in 1955, is distinguished by its hydropneumatic suspension but also by numerous auxiliary hydraulic controls, including that of the semi-automatic gear shifting: gear changes are assisted by hydraulic cylinders and pistons, without a classic mechanical lever directly connecting the driver to the gearbox selector forks.

Paul Magès, the engineer behind the Citroën hydropneumatic system, supervised the development of multiple hydraulic components for the DS during this period, including these gearbox controls.

Archivist's perspective

This drawing illustrates the meticulous work of dimensional definition typical of the Citroën BEA design office in the autumn of 1956: every dimension, every tolerance, every surface finish is specified with millimetric precision, an essential condition for the proper functioning of a closed hydraulic system.

The grouping of two cousin pistons (DS 334-26 and DS 334-43) on the same plate testifies to a logic of documentary economy, common in design offices of the time for parts with similar functions but different sizes.

This part is part of a larger set of hydraulic control piston and cylinder drawings kept in the same file, particularly around the clutch release system: see for example the Drawing of the clutch release control piston D 314-12 or the handwritten divider "54 to 57 — Piston, clutch release cylinder", which show the continuity of these researches on the hydraulic components of the DS during the 1950s.