Citroën technical brochure: the hydraulics of the DS 19, ID 19 and Break

In this document

This illustrated commercial brochure presents the complete operation of the hydraulic system common to the DS 19, ID 19 and Break pp. 146-172, while intentionally excluding the gear change p. 149.

Hydropneumatic suspension

The principle is explained from page 149: each wheel is connected by an arm to a piston sliding in a cylinder, which compresses a gas (nitrogen) contained in a sphere, separated by a liquid. This "pneumatic spring" ensures flexibility p. 149, while a height corrector, actuated by an anti-roll bar, maintains the body-to-ground height constant by adding or removing liquid pp. 151-153.

A valve-based shock absorber, interposed between the cylinder and sphere, limits oscillations by laminating the liquid p. 155, and a dash-pot device prevents untimely corrections by the corrector slides p. 157.

Pressure source and general diagrams

A pump, a pressure regulator and an accumulator provide the pressure necessary for the suspension but also, depending on the model, for the steering, the gear change, and the brakes p. 157. The circuit diagrams p. 159 show that the DS 19 has a main accumulator and a separate front brake accumulator, whereas the ID 19 and the Break use only one accumulator, with power steering remaining optional p. 159.

Power steering

The rack and pinion steering of the DS 19 is assisted by a rotary distributor integral with the pinion, which sends pressurized liquid to a piston connected to the rack p. 161.

Braking

The front and rear circuits are independent: the front circuit is supplied by an accumulator connected to the front suspension, the rear circuit directly by the rear suspension p. 163. A brake pressure distributor proportions the effort according to the vehicle load pp. 163-167. The front brakes are disc — with automatic wear adjustment — and the rear brakes are classic drum pp. 167-168. The ID 19 uses a braking system with two superimposed slides, with metering by back-pressure and spring p. 170.

Page 172 provides a legend for the colours used in all the diagrams (red = high pressure, orange = decreasing pressures, yellow = return/atmospheric, blue = nitrogen).

Context

The DS 19, presented by Citroën at the Paris Motor Show on 6 October 1955, marked automotive history with its stylistic boldness signed by Flaminio Bertoni and the scale of its technical innovations, including the hydropneumatic suspension designed by Paul Magès, who joined Citroën in August 1925 and spent his entire career there, for 49 years, until his retirement in September 1974 (autobiographical notes ; photographs of retirement).

This suspension, later used on the ID 19 (a simplified and cheaper version) and on the Break, would become a lasting signature of the brand, used until the end of the 1990s on several Citroën models. The brochure studied here is part of the general public technical communication intended to explain these then-unprecedented mechanisms.

Archivist's perspective

This document appears to be a piece of technical popularization intended for the public or commercial networks, probably designed to accompany the marketing of the DS 19, ID 19 and Break models. The care taken with the coloured diagrams and the pressure legend p. 172 suggests a pedagogical tool designed to make complex mechanics readable.

It constitutes a visible culmination of the research conducted by Paul Magès from the 1940s on the interactive hydropneumatic suspension, the beginnings of which can be found in the plans for hydropneumatic suspension with differential interaction and automatic levelling dated 17 February 1944, confirmed by the first tests of the 2 CV with hydropneumatic suspension of May-July 1946 and by the test of the 15-Six H of 3-5 April 1954. The continuity between these theoretical studies and the device described here (height corrector, anti-roll bar, spheres) is striking and now documented by these intermediate stages.

The "1956" dating initially proposed is not explicitly confirmed in the transcribed pages; only an uncertain handwritten annotation "56" appears on page 147, which remains compatible with the commercial launch of the DS 19 on 6 October 1955.