Study of an electrically controlled progressive valve (15 June 1970)

In this document

Diagram 1 — the basic progressive valve

Paul Magès sets out the principle of an electrically controlled progressive valve: starting from a pressurized fluid, the aim is to obtain a variable pressure as a function of a force F p. 65.

He details the dimensional constraints of the spool: "the economic dimension is 6.35 mm", i.e., a cross-section of 0.315 cm² p. 65.

Magès specifies that such a distributor could supply an automotive braking circuit, the necessary force then being provided "directly, or via a lever, by the vehicle driver" p. 65.

Diagram 2 — amplification for low signal

For a low-power signal, such as an electrical signal based on engine speed intended to control an automatic clutch, Magès proposes the device in diagram 2 p. 65.

The switching spool is in equilibrium between the force of the electromagnet and that of a spring R2, "these two forces can be chosen to be very weak and of any value" p. 65.

The delivered pressure acts on a piston which compresses a spring R1; the displacement of the piston modifies the tension of R2 until the pressure reaches the value requested by the electrical signal p. 66. Without voltage in the electromagnet, the pressure returns to zero p. 66.

The document is signed "P. Magès" and dated 15.6.70 p. 66, bearing the internal references "P. 6939.1" and "P. 6939_2" p. 65-66.

Context

At that time, Citroën was developing sophisticated hydraulic solutions for its vehicles, inherited from work on hydropneumatic suspension and power-assisted braking of the DS. The idea of an electrically controlled automatic clutch, mentioned here, is part of the research conducted on the semi-automatic transmissions of the time (such as the Citromatic gearbox), without the document establishing a direct link to a specific model.

Archivist's perspective

This handwritten note illustrates a typical Magès approach: starting from a concrete hydraulic regulation problem — here transforming a force or an electrical signal into proportional pressure — and deriving several potential applications (braking, automatic clutch).

The transition from diagram 1 (direct mechanical control) to diagram 2 (amplified electrical control) seems to reflect a progressive shift towards the electrification of hydraulic controls, a theme that extends older work on regulators and distributors kept in the same file, such as the principle of the hydraulic pressure regulator or the 2nd addition to the patent on the flow regulator.

Dated and signed with precision, this document offers a direct insight into Magès' engineering method: rapid sizing calculations, schematic diagrams, and an opening towards future industrial applications.