Handwritten proposal for a constant oil level system for engine crankcases (3 December 1936)

In this document

The proposal

This handwritten note, dated "3-12-36" at the top of the page p. 4, presents a proposal for a system intended to automatically maintain the engine crankcase oil level at a constant height.

The listed advantages

The author lists four advantages to this device p. 4:

1. Eliminating the "dipping that is always unpleasant to do".
2. Maintaining the level "at an optimum height".
3. Avoiding adding oil in small quantities, as the reservoir can hold 8 litres, for example.
4. Allowing precise monitoring of consumption, either by gauging the reservoir, or — a solution deemed preferable — via "a glass sight or a graduated level tube".

A supplementary note considers commercial exploitation: the device "could be fitted as standard or sold as an accessory to the P.D." p. 4.

The schematic diagram

The associated sketch describes an oil reservoir closed by an "airtight cap", connected to the lower crankcase by two vertical tubes: an "Air tube A" and an "Oil flow tube". The operating principle is explained in the legend: oil can only flow from the reservoir when air can enter through tube A, and this air only enters when level B, in the lower crankcase, drops — a balancing mechanism using the communicating vessels/vacuum effect p. 4.

Context

This type of device is part of the classic mechanical maintenance concerns of the 1930s: checking the engine oil level was then done manually, using the dipstick, an operation considered tedious and prone to error.

In December 1936, Paul Magès, who joined Citroën in August 1925 at the age of 17 and a half, had been working there for about ten years as a self-taught technician, technical writer, and then assistant manager of the Super-Control (autobiographical notes); it was only from 1939-1940, with the braking limiter for the TUB van and then his entry into the design office, that he would move towards the work that would lead to the hydropneumatic suspension, the first plans for which date from 17 February 1944 (Hydropneumatic suspension plans with differential interaction (17 February 1944)) and which would be presented on the DS on 6 October 1955. This general context sheds light on the nature of this document — a technical study from his youth related to automotive mechanics —, without anything in the note itself explicitly linking it to that.

Archivist's perspective

This note constitutes a relatively well-developed invention proposal for its format: it sets out not only a technical principle but also its practical advantages and a commercial perspective (standard fitting or accessory sale), which suggests a genuine intention for filing or industrial development rather than a simple workshop sketch.

The principle described — level regulation via an air intake mechanism linked to the drop in level — evokes, through its logic of controlled communicating vessels, a family of reflections that are found later, in a different form, in Magès' work on hydropneumatic circuits.

It is likely that there is a variant or a second copy of this same proposal, dated the same day: see Constant oil level system for engine crankcase — proposal of 3 December 1936 (variant). One can also compare this idea to the sketch of an air/oil tube replacing the oil dipstick, which seems to use a similar principle.