Addendum to the automatic regulation device for hydrostatic transmissions (file 4466)

In this document

Principle of the device

This note, signed by Boucrelle and dated 23 March 1964 (with a second signature dated 25-3-64 on page 70), presents an "addendum to the automatic regulation device for hydrostatic transmissions". It describes a system "allowing the displacement of the pump ① to be limited according to the engine speed" p. 69.

A "spool T", depending on its position, causes a pressure drop in a chamber ③ controlling the pump swashplate. This spool is controlled by two opposing forces: on one side, the oil pressure from a "centrifugal governor ②", nicknamed "Reflex des Tours" p. 69, and on the other, the thrust of a spring compressed by the pump swashplate via a rod ④ p. 69.

Operation and settings

At rest, the spring thrust prevails and the spool puts chamber ③ in communication with the tank; as soon as the centrifugal pressure becomes sufficient, the piston reduces the displacement until equilibrium is reached p. 69.

The text details two adjustment limits, illustrated by a numerical example:

Between these two values, "the displacement variation will be continuous" p. 70.

Stated advantages and reference

The note indicates two advantages: a "pre-selected" gear reduction facilitating acceleration, and increased engine braking at idle compared to the "classic system" at full displacement p. 70. It also specifies that the device "can be adapted to all known similar systems" provided a centrifugal governor is added, and refers to a "sheet No. 4" for adaptation to "Citroën Patent No. 773074 of 25-8-58" p. 70.

Page 71, titled "Page No. 3", bears the corresponding technical diagram, captioned "Displacement limiter diagram", with numbered markers (1, 6, 10, 20, 21, 27, 29, 30, 31, 32, 40, T, R, C) on a drawing featuring a dial graduated in "rpm", a spring, and a lever system p. 71.

Context

File 4466 is part of the research conducted at the B.E.A. Citroën on hydrostatic transmission, a system intended to replace the classic gearbox with a variable displacement hydraulic pump and motor. This work, carried out notably under the direction of Paul Magès, led to numerous tests on 2 CV and 3 CV vehicles in the 1960s-1970s, without resulting in commercialisation.

The cited patent, filed on 25 August 1958, falls under this general knowledge of Citroën patents of the era relating to hydraulic transmissions; the document itself provides no further details.

Archivist's perspective

This technical piece, although the legibility of the manuscript is difficult in places, sheds precise light on a specific sub-component of the hydrostatic transmission: the engine speed-controlled displacement limiter. It appears to be a supplement ("addendum") to a more general regulation device, likely already described elsewhere in the file.

The mention of a reference to a "sheet No. 4" and the 1958 patent suggests that this note is part of a continuous series of engineering work on this subject within the same "Hydrostatic transmission 59-74" file. This document can be compared to the cover page of the "Hydrostatic transmission 59-74" folder, which groups all these pieces together, as well as the handwritten notes "Presentation T.H. 50 CV" at the B.E.A., dated the same year 1964, which could extend this technical reflection.

The diagram on page 71, despite markers that are difficult to interpret in isolation, constitutes a valuable and concrete testimony to the mechanical design methods in use at the B.E.A. in the 1960s.