Diagram of a hydrostatic transmission (ref. E 401 10)

In this document

This single plate presents the complete diagram of a hydrostatic transmission, bearing the reference No. E 401 10 in the technical title block p. 1.

Main circuit

The heart of the system is a variable displacement pump actuating a swash plate, connected to two receivers — right and left — each supplied with high pressure (HP) and low pressure (BP) p. 1. A control valve allows for the selection of three positions: forward ("M A"), reverse ("M A^r") and neutral p. 1.

Regulation and safety

A short-circuit control regulator manages the "start-up short-circuiting", with full opening announced at 600 rpm and closing at 1200 rpm p. 1. There is also a plate inclination retarder towards the overdrive position, as well as a "retarder short-circuiting towards small displacement" device p. 1.

Valve boxes

Two valve boxes are detailed:

• the "main circuit renewal valve box", with a reversing valve and a relief valve calibrated at 10 kg/m² p. 1;
• a second "valve box" comprising a reverse limitation valve (calibrated at 40 kg/m²), two supply valves and a relief valve at 10 kg/m² p. 1.

The document also mentions an accelerator pedal retarder and a low-pressure pump, with the annotation: "The accelerator pedal controls a spring tension and a throttle opening corresponding to a power for a number of rpm" p. 1.

A color legend associates red with HP, dark blue with BP, mauve with "regulated pressure" and yellow with "0 pressure or return" p. 1. The title block, partially cut off, shows "SOCIÉTÉ A[NONYME]... ANDRÉ C[ITROËN]..." p. 1.

Context

Hydrostatic transmissions, which replace mechanical linkages with hydraulic circuits to transmit power and torque, were the subject of research by several car manufacturers in the 1950s-1960s, in connection with the advances in hydraulics applied elsewhere to suspension and braking.

At Citroën, this research is in line with the work on hydropneumatics, a field in which Paul Magès played a central role with the suspension of the DS presented in 1955.

Archivist's perspective

This diagram seems to testify to an in-depth exploration of hydraulic transmissions by Citroën's technical teams, with an obvious concern for precision: the valve calibration values (10 kg/m², 40 kg/m²) and the engine speed thresholds (600 and 1200 rpm) indicate an advanced stage of system definition p. 1.

The complexity of the circuit — two receivers, several valve boxes, multiple regulators — suggests an ambitious, probably experimental project, whose industrial outcome is not attested by this document alone. The incomplete title frame does not allow for further specification of the assignment or the targeted vehicle.