Paul Magès' presentation on hydrostatic transmission and the choice for the “L” vehicle

In this document

This seven-part typewritten file, written by Paul Magès between November 1973 and January 1974, constitutes a true technical plea in favour of the hydrostatic variator over conventional gearboxes.

I — The choice of gear ratios and the advantage of variators

Magès demonstrates, based on comparative calculations on a GS 1220 (3rd, 4th "short", 4th standard, 4th "long"), that no fixed-ratio gearbox can reconcile acceleration, fuel consumption, silence and engine endurance p. 12-15. He concludes that only a continuous and automatic variable ratio system — the variator — solves this dilemma, citing advantages in safety, comfort and economy, with precise figures (up to "20% compared to an automatic gearbox", p. 20-21).

II — Comparison of four transmissions

Tests carried out by the test department (Mr. Satin) in March-April 1973 compare a mechanical clutch gearbox, a torque converter gearbox and two hydrostatic variators (A and B) on a GS 1220: maximum speed at Montlhéry, acceleration, pick-up and road fuel consumption p. 25-30. Variator A, with the "longest" ratio (27.7 km/h/1000 rpm), proves to be the most economical.

III — The choice for the “L” vehicle

Magès argues for a hydrostatic transmission rather than an automatic gearbox studied at Automotive Product p. 32. He details the history of the tests from the test bench of December 1955, the experimental 2 CV running from June 1957 (295,660 km at La Ferté until 1966), up to 13 vehicles totalling 1,130,000 km p. 34-35. The main obstacle remains the noise at start-up, which led to the abandonment of the hydrostatic solution for the “G” vehicle p. 36.

IV to VI — Ancillary applications and perspectives

Magès envisages the hydraulic drive of an alternator, a fan, an air conditioning compressor, or even hydrostatic braking for heavy goods vehicles p. 38-44, as well as new possibilities for the internal combustion engine itself p. 46.

VII — Conclusions

In January 1974, Magès concludes with an economic and human plea, citing F. Rollier twice (15/9/73) on Citroën innovation, and pays tribute to the team working on the project p. 48-49.

Context

The “L” vehicle mentioned here corresponds, in the history of Citroën, to the project that would become the future high-end saloon of the 1970s (the future CX). The general context is that of the first oil crisis (late 1973), which explains Magès' insistence on fuel savings.

The hydropneumatic and hydrostatic transmission is part of the long tradition of Citroën innovation initiated by André Citroën and continued after the war, of which Magès is one of the major figures with the hydropneumatic suspension of the DS (1955).

Archivist's view

This synthetic document, structured as a true engineer's report intended to convince management, is probably one of the most complete pieces for understanding Magès' technical thinking at the dawn of the “L” project. It seems to be a condensation of nearly twenty years of experience (1955-1973), as attested by the summary of tests p. 34-35.

The tone is that of a man conscious of defending a cause against "sceptics" p. 49 and pressed by the industrial schedule — noise at start-up remaining, as he himself acknowledges, the unresolved point p. 36.

This file finds a direct echo in the Handwritten note "Problem transmission vehicle L" written a few days earlier, as well as in the Record of mileages of test vehicles with Hydrostatic Transmission, which precisely documents the figures cited on page 35.