Périneau Note no. 4: regulation of a hydrostatic converter (29-12-65)

In this document

This handwritten technical note by Périneau, dated 29 December 1965, describes in four parts the operation of the regulation of a hydrostatic converter, illustrated by a complete schematic diagram p. 68.

I. The regulator

The spool of the regulation distributor "D" is in equilibrium between an input force f(θ), linked to the throttle opening angle, and a pressure force f(N) from a centrifugal distributor, a function of engine speed. This spool feeds the working cylinder "V", coupled to the swashplate of the hydraulic generator p. 65. The goal is to tend towards the equilibrium "Engine torque = Generator resistive torque": at equilibrium, the vehicle travels at a stabilized speed; otherwise, it accelerates or decelerates p. 65.

II. The correction network (feedback)

A piston "A", integral with spool D, and a jet "G₁" with low pressure drop introduce an additional feedback force, active in the "4th → 1st" direction of the cylinder piston V, associated with a retarder (elastic capacity "E") p. 65-66. In the opposite direction (1st → 4th), which is slower and requires timing linked to driving, no feedback is provided: it is the timing jet "G₂" that acts as a damper p. 66.

III. The clutch

The spool of the distributor "F" is in equilibrium between f(N) and a spring "R2". It controls the bypass between the two main lines of the converter. At idle, a low driving pressure corresponds to the "licking phase"; then comes the synchronization phase, where the flow is distributed between the driving path and the slip path, until the latter is cancelled at a fixed engine speed, marking the end of the clutch engagement p. 66-67.

IV. The downshifter

It aims to avoid maintaining a high gear ratio at low engine speeds. The spool "H", in equilibrium between a spring "R3" (compressed according to the generator displacement) and f(N), switches the regulated pressure chamber of cylinder V to the tank return. Each engine speed corresponds to a maximum generator displacement, and therefore a maximum gear ratio, decreasing with engine speed p. 67.

The final diagram p. 68 labels all the reference marks: f(θ), BP (low service pressure), PR (regulated pressure), R (tank return), f(N), and locates the components C, D, E, F, G1, G2, H, V, R2, R3.

Context

The hydrostatic converter mentioned here is part of the research conducted by Citroën, under the impetus of Paul Magès, to develop an automatic transmission without a conventional mechanical clutch, combining a hydraulic generator and motor with variable displacement. This work, carried out notably at the B.E.A. in the 1960s-1970s, aimed to equip popular vehicles (2 CV, 3 CV) or more ambitious ones ("L" vehicle) with a continuous transmission.

Archivist's perspective

This note constitutes a rigorous and synthetic theoretical exposition of the regulation principle, probably intended to formalize in writing a solution already tested on a bench or vehicle. The repeated signature of Périneau on each page p. 65-67 suggests an official working document, carefully validated and dated.

The level of detail — four articulated subsystems (regulator, feedback, clutch, downshifter) — and the summary diagram p. 68 make it a pivotal piece for understanding the control architecture of the hydrostatic transmission, prior to subsequent tests and presentations such as the Handwritten notes "Presentation T.H. 50 CV" at the B.E.A. or the Endurance test monitoring of the 2 CV A12.