Note by P. Magès: adapting the engine to the automatic ratio variator (P.7994, 16.12.1973)

In this document

The principle: freeing the engine from the compromise of stepped gearboxes

Magès starts from an observation: engines are designed to adapt to stepped gearboxes, which forces the power curve to be "bulged" and limits the compression ratio to the requirements of low engine speeds p. 50.

With a continuous and automatic ratio variator, this dilemma disappears: "you press the accelerator and the variator automatically adapts the ratio" to seek power where specific consumption is lowest p. 50.

Proposed modifications

Magès proposes, for an engine running at, for example, 6000 rpm:

• increasing the compression ratio at maximum speed to gain power and thermal efficiency p. 50;
• or, without seeking this gain, reducing the diameter of the carburettor nozzle to limit filling and promote mixture preparation at low speeds p. 51;
• automatically limiting filling according to speed, so that "the pressure at the end of compression cannot exceed the acceptable limit" — which amounts to aiming for a constant end-of-compression pressure across the entire curve p. 51.

The result is a power curve that is "more rectilinear and perhaps even concave", with no disadvantage when using a variator p. 51.

Expected benefits and implementation

Magès anticipates a "significant reduction in consumption" and, probably, a gain in pollution "due to the improvement in combustion" p. 51.

Technically, it is sufficient for the variator's servo-control device to engine speed to command "the displacement of a cam of appropriate profile serving as a throttle opening stop" according to a pre-established law (underlined word, p. 51) — a law that can be adapted, by simply changing the cam, to the type of fuel (regular petrol), altitude, or temperature p. 52.

He considers the implementation "within the reach of any person skilled in the art" p. 52.

Priority and technical exchange

Magès notes that these principles had already been discussed on 13.12.73 with a "Mr. Alfieri" [uncertain, possibly Maserati] p. 52, and refers to an earlier report from 24 December 1956 (no. 561221/224, § 15-16-17), microfilmed under the references P1618-1 to P1618-8, which would already succinctly describe these proposals p. 52.

Context

This note is part of the research conducted at Citroën on hydrostatic transmission, an alternative to conventional gearboxes that Paul Magès and his team had been developing since the early 1960s.

The name cited, "Alfieri", historically evokes the Maserati family (Alfieri Maserati, founder of the brand), but the uncertainty of reading the transcription requires the greatest caution: nothing in the document allows this connection to be confirmed with certainty.

Archivist's perspective

This three-page note (P.7994.1 to .3) is of particular interest: it describes not only a mechanical device, but an engine design philosophy made possible by the continuous variator — rethinking the power curve itself rather than submitting to it.

The explicit reference to a 1956 report p. 52 suggests that Magès considered these ideas to be long-standing in his personal thinking, potentially dating back to the beginnings of his work on hydrostatic transmission. This 1973 document would then be a reformulation or a re-emphasis, probably in the context of the discussions on the L vehicle that occupied Magès during the same period.

It can also be compared to Magès' technical presentation at the B.E.A. from the same period, which probably synthesises all these reflections on hydrostatic transmission.