Citroën Patent No. 833,391 (1960): servo-control of a hydro-electric unit motor

In this document

This is a French patent application filed by the Société Anonyme André Citroën on 19 July 1960, under the provisional number 833,391, with the mention "issuance adjourned" p. 92. The invention concerns a "servo-control device for the motor of a hydro-electric unit" p. 92-93.

Principle of the invention

The text specifies that the targeted motor is "of a type comprising a swashplate whose inclination controls the power and a hydraulic cylinder for adjusting this inclination" p. 93. Means allow this cylinder to communicate either with the high pressure of the hydraulic circuit or with the exhaust, depending on the value of certain quantities p. 93.

These quantities can be "power, voltage, intensity, speed, or even temperature" p. 93. The device can also follow "a pre-planned program" rather than a simple fixed value p. 93.

Detailed operation

Page 94 describes the case of voltage: when the generator voltage reaches a sufficient value, a coil puts the cylinder to exhaust, returning the swashplate towards its neutral position under the action of a return spring, which reduces the power and restores the desired voltage p. 94.

For regulation related to the battery, several variants are exposed: a bellows thermal probe measuring the battery temperature p. 94, a two-coil assembly where one is controlled by a thermal bimetallic strip p. 94, or even a bimetallic strip acting mechanically on the core p. 94.

The final summary p. 95 repeats these points in the form of numbered claims, mentioning in particular a "spool valve" controlled by the quantities in question and regulation "thermistors" appearing on page 99, associated with a handwritten note referring to "figure 4 main patent".

The plates p. 97-98, 100, 102 present the diagrams Fig. 1 to Fig. 4, with numbered markers (swashplate 5, cylinder 4, valve 3, generator 2, hydraulic motor 1, battery 24).

Context

Let us recall, as context external to the document: from the 1950s, Citroën developed innovative hydraulic systems (hydropneumatic suspension, steering, brakes), and Paul Magès was its iconic engineer. The "hydro-electric units" mentioned here — a hydraulic motor driving a generator — are part of a broader logic of using pressurized fluid as an auxiliary energy source on vehicles, complementary to the suspension applications better known to the general public (DS 1955).

Archivist's perspective

This patent illustrates a lesser-known aspect of Citroën's research at the time: beyond suspension, the company sought to exploit hydraulic energy to regulate auxiliary electrical equipment (generator, battery). It seems that this device is part of a broader reflection on hydrostatic transmission, traces of which can be found in later work from the same laboratory, such as the Handwritten notes "Presentation T.H. 50 CV" at the B.E.A. or the P. Magès' presentation on hydrostatic transmission.

The presence of several variants (voltage, temperature, bimetallic strip, thermistors) suggests iterative engineering work aimed at covering a maximum number of use cases, probably to strengthen the legal scope of the patent. The handwritten name "M. Riffaut" p. 101 could designate a collaborator or an agent, but his exact role is not specified in the document.