Diagram D.73 — Hydraulic gear control and clutch circuit (DS, 1960)

In this document

This technical plate, referenced Diagram D.73, is titled "GEAR CONTROL AND CLUTCH CIRCUIT" and illustrates a specific operating case: "4th gear engaged, engine speed 700 rpm, pressure in front brakes > 10 kg/cm2".

The sub-assemblies represented

The diagram details several hydraulic and mechanical components in cross-section:

• The hydraulic block, including a "Pre-selector spool", an "Automatic gear control spool", a "Manual clutch control" and an "HP inlet" (high pressure).
• The flow regulator, in the central position, represented in cylindrical cross-section.
• The centrifugal regulator, on the right, with its annotations "Purge screw", "regulator brakes", "Return to reservoir", "FR brake caliper", "Re-engagement lock" and "Start speed adjustment".
• A "re-engagement corrector" (handwritten annotation, with the marked "3" underlined), connected to a "throttle shaft (carburetor)".
• A "clutch release cylinder", accompanied by a handwritten annotation mentioning a clearance "at the radius" [uncertain value].
• The "gearbox cover", in cross-section, with parts numbered 1 to 4 and "AR".

Handwritten annotations

The document bears several handwritten notes: "re-engagement corrector" and underlined "3", "throttle shaft (carburetor)", a mention relating to a clearance of a few microns at the clutch release cylinder, as well as a barely legible note mentioning a "return in +" near the hydraulic block. A red line without text also appears near the centrifugal regulator.

The bottom of the diagram bears the mention "DS. 1st Synchronized".

Context

The title of the archive links this diagram to a notable evolution of the Citroën DS transmission: the replacement, around 1960, of the low-pressure pump by a centrifugal regulator in the hydraulic gear control and clutch circuit.

This semi-automatic hydraulically controlled transmission, without a clutch pedal, constitutes one of the characteristic innovations of the DS, in the continuity of the work of Paul Magès on hydraulics applied to the automobile — a field where he is best known for the hydropneumatic suspension.

Archivist's perspective

This diagram D.73 illustrates, in technical detail, the operation of the combined gear/clutch circuit at a precisely defined moment of operation (4th gear, 700 rpm, brake pressure > 10 kg/cm2), which suggests a use for tuning or technical training rather than a general presentation plate.

The handwritten annotations — re-engagement corrector, clearance at the clutch release cylinder, barely legible note on a "return" — suggest that this document served as a working aid, probably annotated during tests or checks on the circuit p. 1.

The mention "DS. 1st Synchronized" at the bottom of the plate seems to place this diagram in the context of a precise evolution of the DS gearbox, but its exact meaning is not specified in the document.