2nd addition to patent P.685.691: a flow regulator with perforated discs (1956)

In this document

Purpose of the text

The document, dated 20 January 1956, constitutes the 2nd addition to patent P.685.691 of 15 February 1955 p. 9. It specifies that one must "resume the text of the first addition up to page 2, line 10", then continue with a new development p. 9 — the text therefore presents itself as the continuation of an already initiated patent file.

The problem posed

It is a matter of ensuring, in a gear mechanism, a correct succession of movements ("declutching, shifting to neutral, synchronisation, gear shifting, re-engaging"), which assumes a "regular filling of the capacities (13) over time" and therefore a "sufficient constancy of flow" p. 9.

A first addition had already attempted to respond to this with a by-pass mounted in parallel with a "helical resistance (59)", intended to compensate for backpressures linked to viscosity, "especially when cold" p. 9. The present text proposes a solution deemed more precise.

The principle: pressure drop in a thin wall

Drawing on Poiseuille's formula, the text explains that the pressure drop of a conduit is broken down into a term linked to viscosity (proportional to length) and a term linked to kinetic energy. For a "thin-walled" orifice (zero length), only the second term remains: by keeping the upstream-downstream pressure difference of the orifice constant, a substantially constant flow is obtained p. 9.

Description of the regulator

The device comprises a hollow piston (1) containing thin perforated discs (2), each holed at (3), forming successive chambers; the assembly is housed in a body (4) with inlet (5) and outlet (6) pipes, and a calibrated spring (7) p. 10.

The operation described: the pressurized fluid passes through the holes (3), the resulting pressure drop acts on the piston which, under the effect of the upstream/downstream pressure difference, compresses the spring (7) until it occupies position (9) and partially closes the outlet (6), thus regulating the flow to a stable value even if the intake pressure varies p. 10.

Context

The patent P.685.691, filed in 1955, concerns a gear-shifting mechanism linked to the hydraulic work of Paul Magès for Citroën, where he joined in August 1925 and where he would spend 49 years, first as a self-taught technical writer and then as deputy head of the Super-Control before joining the design office (autobiographical notes). This second addition, dated January 1956, is part of the development period of what would become the DS, presented on 6 October 1955. The use of Poiseuille's formula and pressure drop regulators is a classic hydraulic engineering approach of the time, but nothing in this document explicitly links the invention to a specific vehicle model.

Archivist's perspective

This document clearly illustrates the iterative work of patent filing: it is not an isolated invention but the second successive improvement of the same mechanism, the first having used a by-pass deemed less precise p. 9. The perforated disc regulator thus seems to correspond to a technical refinement seeking simplicity of manufacture ("simple construction") while gaining in precision p. 9.

The attached sketch p. 10, although summary, allows for the visualisation of the equilibrium position of the piston (mark 9) which is at the heart of the self-regulation principle.

This text finds its place in the same hydraulic design effort as other pieces in the collection, notably the Principle of the hydraulic pressure regulator, which also deals with the regulation of pressurized circuits, or the Schematic diagram of the DS 19 hydraulic circuit, which provides a broader overview of the system into which this type of component could be integrated.