Lachaize note on brakes, the AP, the 3 CV, the FZ, the future DS and the S vehicle (1966-1967)

In this document

Brakes in the wheels or at the gearbox output

The file opens with a question posed to "Mr. Lachaize" and dated "7.66": should the brakes be placed in the wheels or on the transmissions p. 73?

A list of arguments in favour of gearbox output brakes follows: easier controls, disc diameter limited only by ground clearance, lower longitudinal reactions on the ball joints, no protection against water and mud required p. 74. "Points to be debated" are noted: cooling, increase in unsprung weight, attitude correction during braking p. 74.

Conversely, a second list, dated "22-7-66", details the advantages of brakes in the wheels: less angle and fatigue on the transmissions, less constrained pivot, possibility of "anti-lock" systems, better cooling of the discs thanks to the thermal inertia of the wheels, reference to "the melting of the delrin of the tripod ball joints on AP at Ventoux", reduced rotational inertia of the gearbox, possibility of lowering the centre of gravity, and long-arm parallelogram axles p. 75. Three handwritten remarks complete this debate, one of which refers the problem to "Mr. Bourgeron" p. 76.

"The A.P. as I saw it"

A text signed and dated "5.1.67", presented as an older report written "after 18 months of BEA" p. 77, describes an AP designed in the spirit of the 1948 2 CV: minimum vehicle, 2 CV engine modified for torque (3.3 mkg at 3000 rpm), 4-speed gearbox, unladen weight of 450 kg, 125×330 tyres p. 77. The author also mentions the future of the 2-stroke direct injection engine, with a marginal note specifying that it is "not yet in 1967" because of the price of injection and pollution p. 77.

He advocates for brakes in the wheels, a parallelogram front axle, a constant-velocity transmission with tripod and Rzeppa joints (compared to the Austin 850 and the Lancia Flavia), a classic suspension on silent-blocks inspired by the Lancia Flavia and the Renault R4, a body derived from the 2 CV with a tailgate and an "R4-style" platform p. 78-79. A sketch of the car's silhouette accompanies the text p. 79, signed "Vauhaize" [uncertain reading] and dated "14.5.62" p. 79.

The 3 CV: desired developments

Four customer complaints are listed: appearance, noise, gearbox (1st gear synchro), steering stiffness and roll p. 80. Remedies are proposed: round headlights, sliding window doors, noise control (M.28 engine, single exhaust pipe, Rzeppa joints), a quieter "direct" gearbox, and criticism of a "solid friction" introduced into the steering linkage p. 80-81. The author proposes front and rear anti-roll bars and 14-inch wheels to reduce steering stiffness p. 82, and rejects the "A.2000 programme" consisting of mounting a 3 CV engine on a 2 CV body p. 82. The text is dated and signed "5.1.67" p. 82.

The FZ: development

The FZ is presented as having to replace the coexistence with the F vehicle, a competitor to the AM p. 83. The following are considered: redesign of the rear, adoption of the frame at the rear, retention of the flat 4-cylinder rather than the NSU engine, and a critique of the main defect of the hydraulic suspension — the "slow galloping movements" p. 83-84. Two remedies are proposed: an anti-dive front axle and an axle allowing roll without influencing the trajectory, as on the 2 CV or the 15 p. 84. The text, dated "5.1.67", bears a printed fragment "ANDRÉ CITRO..." in the header p. 84.

The future DS

The document considers two competing prototypes: one using a pivot in the axis, gearbox output brakes and a 30° V-engine (8 and 6 cylinders); the other with an inclined inline 6-cylinder, brakes in the wheels, gearbox outputs under the crankshaft and gearboxes equipped with a converter p. 85. A comparison is made with the Pontiac inline 6-cylinder overhead camshaft engine p. 86.

The S vehicle

The text questions the interest of adapting the "M engine" (bulk, 24 mkg of torque) when the S vehicle, "tinkered with" by "Mr. Né", pleased customers for 3 million with a minimum of investment p. 86. Dated "5.1.67" and signed, the signature being read with uncertainty as "Magès" p. 86.

Context

The reader should know, outside of the document, that Paul Magès is the Citroën engineer who invented the hydropneumatic suspension, whose first plans date back to 17 February 1944 and which was adopted on the DS presented on 6 October 1955 (hydropneumatic suspension plans, test of the 15-Six H). In 1966-1967, the date of this document, he was a self-taught man who had become deputy head of Super-Control within the design office, having joined Citroën in August 1925 and remaining there until his retirement in September 1974 (autobiographical notes). The acronyms mentioned refer to internal Citroën projects of the time: the AP (future small car project, which would notably lead to the Dyane), the FZ (which would become the CX), and the S vehicle (probably linked to the future GS or an intermediate model). The 3 CV here refers to the Dyane or a derivative of the 2 CV in project at that time. The comparison with American engines and the Pontiac 6-cylinder reflects the technical debates of the 1960s on future engines.

Archivist's view

This composite file brings together several technical reflections, probably written or commented on by Paul Magès himself in January 1967, concerning the future of several Citroën ranges simultaneously p. 77, 82, 84, 86. The final signature, read with caution as "Magès" p. 86, and the very personal tone of the texts ("I repeat myself", "I do not believe") suggest an author accustomed to expressing himself in his own name on architecture choices — consistent with the position of deputy head of Super-Control that he then occupied at the design office (autobiographical notes).

It seems that this document well illustrates Magès's working method: starting from a concrete technical observation (brakes, transmissions) to go back up to choices of global vehicle architecture, with the constant concern of preserving the qualities of comfort and simplicity inherited from the 2 CV. The criticism of the "galloping" of the hydraulic suspension p. 83-84 is particularly interesting because it shows a critical look by the inventor at his own invention.

This file naturally extends older reflections on hydraulic or pneumatic suspension and on road tests of hydraulic anti-roll, by applying them here to the prospective of future Citroën models.