Technical Notice E.42401 G — Double switch and bimetallic relay (February 1944)

In this document

This Citroën technical notice, referenced No. E.42401 G, describes a device called "Double switch and bimetallic relay", composed of 3 sheets p. 15-17, accompanied by a handwritten diagram of an experimental assembly dated 21 February 1944 p. 18.

Mechanism description

A lever A, animated by a "regular alternating movement of amplitude α", touches two deformable levers C and C' alternately, mounted on a part D pivoting around a center O p. 15-16. Two identical bimetallic strips B and B', heated by resistors R and R', close alternately according to this contact; their spacing e is adjustable by a screw V, and a lamp L allows checking the moment of their contact p. 16.

Operation

The text explains that if the frequency of the movement of A is high, the spacing e remains stable; if it decreases, the bimetallic strips heat up and cool down alternately, causing e to vary at the same frequency as A. By pivoting part D by an angle β, the contact times are unbalanced "in favor of C'", causing the contact between B and B' to close p. 16.

Application conditions

The notice sets precise requirements:

Finally, a usage condition specifies that "lowering must only be controllable on the condition that at least 2 wheels request it at the same time", and that these two wheels must not be diagonally opposite p. 15. The electrical diagram on page 15 shows inputs "AV G" (Front Left), "AR D" (Rear Right) and outputs "to the electro-distributors", with markers R (Raising) and A (Lowering).

Sheet 2 p. 18 provides a handwritten diagram of the experimental assembly, signed and dated 21 February 1944, using the same markers (α, A, C, C', D, β, O, B, B', R, R', L). The validation stamps bear the mentions "Cont. SERE JARI 24/2", "Vér. ROGUEL" and "Etabli MAGÈS", dated 24 February 1944 p. 15-16.

Context

This type of bimetallic switch is part of the research conducted at Citroën during the Occupation on automatic suspension control systems, which would lead after the war to the hydropneumatic suspension equipping the Traction 15-Six H (1954) and then the DS (1955). The notion of "lowering" and "raising" evokes the leveling correction functions that will be found on these vehicles. The principle of the bimetallic strip (deformation by differential electrical heating) was a common time-delay relay technology at the time, here diverted to create a logical time delay linked to wheel load.

Archivist's perspective

Dated late February 1944, this document is situated in a period of intense research on leveling suspension, as evidenced by the List of problems under study as of 22 February 1944, established two days before the validation of this notice. The experimental diagram p. 18, dated 21 February 1944, seems to have shortly preceded the formalization into an official notice on 24 February.

It is likely an electromechanical component intended to secure the suspension lowering control, by preventing a single wheel from triggering the movement — a safety logic found in the spirit of the Hydropneumatic suspension plans with differential interaction of the same week. The open question at the end of the notice ("What are the necessary characteristics...?", p. 17) suggests that this document served as specifications transmitted to a supplier or a design department, rather than a definitive solution.