Patent P 5069 — Automatic headlight orientation in corners (8 June 1965)

In this document

This descriptive memorandum, dated 8 June 1965 and referenced P 5069, presents an invention intended to automatically orient additional headlights (mounted in addition to the regulatory lights) when the vehicle enters a corner while using high beams p. 54.

The problem posed

The text starts from a simple observation: low beams ("dipped beams") provide sufficient illumination in corners at low speed, but high beams, being more "focused", leave the corner insufficiently illuminated at high speed. The idea is therefore to orient, in corners, the long-range projectors normally reserved for straight lines p. 54.

The three conditions to be satisfied

1. In a standard corner, both projectors must remain "substantially parallel" and steer faster than the wheels, by a defined value p. 54.
2. In a very tight corner (mountain roads, parking, full lock), the projectors must steer "almost at a right angle", with an angular offset between them p. 54.
3. The vehicle's roll in a corner raises the headlight beam; this is compensated for by tilting the axes of the projectors, low point towards the front, according to the vehicle's roll flexibility (angle ∠11, figure 4) p. 55.

Mechanical solution described

The device takes its movement from the steering relays, by exploiting the "laws of cosine variations" p. 55, 57. Figures 3a-3c detail an articulated lever on the right side (reference marks 1 to 5, 23), with radii R7 and R10 and setting angles (23°/16° then 43°/6° depending on the pages) p. 55-56.

The movement of the cable or rod is then corrected by a cam mounted on the headlight articulation axis: at the start of the steering, the cable winds onto a small radius R12 (fast movement), then onto larger radii R13 and R14 at the end of the travel (slower movement) p. 57.

An angular correspondence table (fig. 2, p. 59) gives increasing α1/β1/α2/β2 values, for example 6°/10'½/6°/15' up to 37'½/45°/42°/63'½, illustrating the relationship between the angle of the front wheels and the angle of the headlights.

The text specifies that the principle can also be achieved "hydraulically or pneumatically by pistons and levers", the steering-headlight connection then being made "by tubes", and that the headlight axes can be extended to carry fog lights p. 58.

Context

This patent belongs to a period when Citroën, via the engineering of Paul Magès, was generalizing the hydraulic solutions inherited from the DS to other vehicle functions. The hydropneumatic suspension and power steering of the DS were already based on principles of movement transmission by pressurized fluid; it is therefore not surprising, as a general context, that a directional lighting device would consider a hydraulic or pneumatic variant.

Historically, the orientation of headlights according to steering will become an iconic feature of the DS (directional headlights), made famous by the 1967-1968 version. This 1965 patent, which predates it, shows a stage of technical reflection on the subject — a study that remains documented here only in its mechanical form using levers and cams, with a hydraulic variant only mentioned at the end of the text.

Archivist's perspective

This technical memorandum is distinguished by its almost exclusively mechanical precision: levers, cams, radii, and angular settings are described with a concern for kinematic justification ("laws of cosine variations", p. 55, 57) rather than through a hydraulic approach, even though Magès is best known for his hydropneumatic inventions.

It seems that this patent represents a design phase where the mechanical solution using cable and cam is favored, with the hydraulic option only mentioned at the end of the document as an alternative possibility p. 58. The angle tables (fig. 2, p. 59) suggest an already advanced engineering effort, with tests of numerical correspondence between wheel steering and headlight orientation.

This document is in line with the work carried out at the design office on safety and driving comfort, as a continuation of other studies from the same period, such as the BBC meeting summary of 22 February 1962 or the BBC conferences Nov.-Dec. 1960, which testify to the same concern for the continuous improvement of DS devices.