Magès Note no. 560.331: first hydraulic transmission diagram (4 April 1956)

In this document

This handwritten note, numbered 560.331 and dated 4 April 1956, is signed with the stamp "[P.]MAGÈS". It is titled HYDRAULIC TRANSMISSION and consists of two parts, with a ".../..." reference indicating a continuation not provided here.

1°) General diagram

Magès outlines two possible setups:

• Solution A: a variable-displacement volumetric pump, driven by the vehicle's engine, supplies a hydraulic motor placed at each drive wheel. The transmitted torque is identical for each wheel, but "the maximum transmitted torque cannot be greater than the resistive torque of the most disadvantaged wheel", similar to a classic mechanical differential p. 163.

• Solution B: two separate generators, each supplying a hydraulic motor, advantageously placed "at both ends of the crankshaft" to reduce torsion. They deliver an identical volume at every moment. An "equilibrium pipe" allows for pressure balancing when cornering; a device can limit the passage of fluid there "to the value necessary only to account for the difference in flow required on the right and left when cornering". In difficult cases, "a valve can interrupt the passage of the fluid" p. 163.

2°) Generator flow adjustment

This section, unfinished on the page, introduces a technical diagram: an inclined plate connected to an XX axis, forces noted F1 and F2, an "ENGINE shaft", arrows "RETURN" and "To the RECEIVER(S) (Hydraulic motors)", as well as an angle α. The only written point indicates: "At engine idle, the plate must be perpendicular to XX" p. 163.

Context

This note dates from 1956, a period when Citroën had just launched the DS (1955) with its hydropneumatic suspension, another invention by Paul Magès. A hydrostatic transmission — replacing classic mechanics (gearbox, shafts, differential) with hydraulic pumps and motors — represented an ambitious research path at that time, pursued by Citroën for several decades, notably on the GS and "L" vehicles in the 1970s.

Archivist's perspective

This document appears to be one of the very first written formulations of the hydrostatic transmission concept by Magès, almost twenty years before the more advanced developments attested in the "Hydrostatic transmission 59-74" file. The diagram for solution B, with its two generators and its differential torque management per wheel, likely prefigures the architectures studied later.

The mention of the ".../..." reference indicates that the rest of this note (development of flow adjustment) is missing, likely kept on a following page of the same file.

This initial sketch can be compared to later works kept in this same collection, such as the P. Magès presentation on hydrostatic transmission or the Citroën Plan E 3091 of the hydrostatic transmission of the L vehicle, which illustrate the culmination, almost twenty years later, of this idea sketched in 1956.