DS 314-12 clutch control piston drawing (Citroën, 1957)

Dimensioned technical drawing of the DS 314-12 clutch control piston, with its form tolerances (run-out, chamfers, spherical radius) and the Citroën design office validation block dated 4 January 1957.

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Understanding this document

In this document

This technical drawing presents the clutch control piston for the DS, reference DS 314-12, drawn in section with its material hatching p. 15.

Main dimensions

The drawing details several geometric dimensions:

a 35° chamfer (blunted angle), with a "0.35 to 0.65" transition;
a spherical radius of 3.25;
an internal conical recess of approximately 120°, with a zone where a "centre or nipple" is explicitly prohibited;
lengths dimensioned "1±0.3" and "3.75±0.25", as well as an overall dimension "28.5± 0.15" p. 15.

A header table specifies a form tolerance requirement: the maximum run-out relative to diameter Ø1 must not exceed 0.1% (mark F14) p. 15.

Validation block and approval

The validation block identifies the part as "PISTON DE COMMANDE DE DÉBRAYAGE" (Clutch control piston), attached to the DS314_02 assembly, in C4 steel with a treatment noted "G (0.2)" and no coating p. 15.

The validation circuit indicates a drawing dated 28.12.56 (Bourget) followed by a verification dated 4.1.57 (Belloncle), under BEA plan no. DS 314-12, sheet 1/1, launched by note no. 28311, with a modification "(m1) 4 — 28851" p. 15.

Context

The DS, presented by Citroën in 1955, incorporates a hydropneumatic suspension system from which a set of auxiliary hydraulic controls is derived, such as power-assisted clutching. This type of part, a hydraulic cylinder piston, belongs to the technical world developed by Paul Magès' teams around this cutting-edge technology for the time.

The "C4 steel" mark refers to the grades of structural steel commonly used in the French automotive industry at the time.

Archivist's perspective

This drawing dated 4 January 1957 (verification visa, p. 15) is likely a revision of the same component already documented in 1954, as evidenced by the 1954 D 314-12 clutch control piston dimensioned drawing. The evolution of the reference from "D 314-12" to "DS 314-12" likely illustrates the adaptation of this part to the new DS range.

The strictness of the form tolerances (0.1% run-out) and the explicit prohibition of a "centre or nipple" on the conical zone testify to the care taken in the machining of this precision part, essential for the proper functioning of the hydraulic assistance system.

This plan is part of a coherent set with the 1957 DS 314-02 clutch cylinder drawing, to which this piston is clearly intended to be associated.