Sheet dated 10 May 1933: study of the differential mechanism and the planet gears

In this document

This sheet dated 10-5-33 (10 May 1933) bears the number "6" circled and consists of two pages: a sketch accompanied by a table p. 38 and a second supplementary sketch p. 39.

The sketch and its reference letters

The diagram on page 38 represents a mechanism with a horizontal shaft marked M, connected to an assembly annotated S, b, l and B, the latter referring to a circle marked "E.M.B.". Curved arrows indicate directions of rotation on discs. The handwritten text at the top of the page, although uncertain, evokes the case where "the two wheels move in the same direction": for two identical speeds, the planet gear (S) would be "free in both directions", while a speed difference between the wheels would move it "in the direction of the arrow".

The table of six cases

A table summarizes six configurations numbered from 1° to 6°, crossing the state of the "Ped acc" (accelerator pedal?), the engine, the engaged gear and the behavior of the planet gear S. Several lines specify that "M - B and l rotate at the same speed" leads to "S in - free", while other cases (progressive engagement, minimum governor) are associated with "S free". The last line mentions an "automatic" operation in 1st gear.

The page ends with a paraph read as "E. Dup." p. 38.

The second sketch

Page 39 shows a supplementary drawing: a crenellated cam-shaped part connected to the shaft M, a set of discs crossed by a vertical axis, and a reference B at the end of a horizontal line. "–" and "+" signs frame the vertical axis, without an associated explanatory legend in the document.

Context

A classic automotive differential distributes engine torque between the two wheels of the same axle while allowing different rotation speeds, particularly when cornering — this is the role of the planet gears, those small pinions internal to the mechanism.

This sheet belongs to a set of handwritten studies that Paul Magès seems to have conducted in 1933 on various mechanical components (gears, injection, carburetor, synchronizer), as evidenced by the cover folder found in the same file. However, nothing in the document allows this mechanism to be linked to a specific Citroën project or vehicle at that date.

Archivist's perspective

This sheet illustrates an engineer at work: methodically breaking down, case by case, the behavior of a differential according to engine speeds and acceleration states p. 38. The systematic numbering of the six configurations and the reference to a second explanatory sketch p. 39 testify to a concern for completeness in mechanical analysis.

It seems that this study belongs to a broader series of reflections on transmissions and engine speeds conducted by Magès during this period, as suggested by the handwritten folder "1933" listing several related subjects. The presence of a distinct paraph ("E. Dup.") at the end of page 38 invites caution: the document could result from collaborative work, without the exact role of each participant being specified.