Swiss Patent No. 291970 (Daimler-Benz) — automatic height corrector, 1953

The complete fascicle of the Swiss patent filed by Daimler-Benz, describing five hydraulic, mechanical or electrical variants of an automatic vehicle height corrector — a competitive intelligence document kept in the Magès collection.

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Understanding this document

In this document

This fascicle is the main Swiss patent No. 291970, filed by Daimler-Benz Aktiengesellschaft (Stuttgart-Untertürkheim) on 22 March 1951 and published on 1 October 1953, under the title « Vorrichtung zum selbsttätigen Einhalten der Bodenhöhe an Fahrzeugen » ("device for the automatic maintenance of vehicle ride height") p. 14. The applicant's representative is Fritz Isler, Zürich p. 20.

Problem posed and principle of the invention

The introductory text explains that vehicles intended for many passengers, particularly buses, suffer from floor height variations depending on the load, a problem aggravated by a soft and comfortable suspension p. 14. A manual hydraulic or pneumatic control solution already existed; the invention aims instead for an automatic corrector: means react to any change in distance between the body and the road to compensate for it without driver intervention p. 14.

Five variants described

The patent details five embodiments, all based on the same principle (a control spool connected to the axle detects the deviation and drives a cylinder or a motor):

Figure	Type of correction	Locking/unlocking	Page
Fig. 1	Hydraulic cylinder on spring stop (rigid axle)	Hydraulic, active only when stationary (pump 33 on transmission shaft)	p. 15-16
Fig. 2	Two hydraulic cylinders on leaf spring	Friction ring 37 on the drive shaft	p. 16-17
Fig. 3	Common cylinder via bell cranks on leaf spring	Speed governor (tachometer) 59	p. 17
Fig. 4	Cylinder acting on the axis of rotation of a trailing arm (independent wheels)	Same hydraulic principle	p. 18
Fig. 5	Torsion bar adjusted by an electric motor via worm gear	Electric switch 67, cut by a switch 78 when driving	p. 18-19

In all cases, the device only acts when stationary or at low speed, in order to avoid permanent pumping of the body while driving — a defect considered annoying by the authors p. 16.

The claims (Patentanspruch and 12 sub-claims) cover hydraulic, mechanical, electrical and pneumatic correction, as well as the various locking/unlocking methods linked to the vehicle's movement p. 19-20.

Pages 21-22 reproduce the technical diagram plates (Fig. 1 to 5) without additional descriptive text.

Context

This Swiss patent is the local counterpart of an application filed by Daimler-Benz in Germany in the early 1950s — a period when several manufacturers were independently seeking solutions for automatic ride height correction, while no integrated hydropneumatic system like the one Citroën would develop yet existed on the market. At Citroën, these researches are precisely those led by Paul Magès, who joined the design office in 1939-1940 and was the author, as early as 17 February 1944, of plans for hydropneumatic suspension with differential interaction (plans of 17 February 1944); the first tests on 2 CV would follow in May-July 1946 (notebook of the first tests).

This type of document illustrates the technical effervescence surrounding automotive suspension in the immediate post-war period: heavy goods vehicle and passenger car manufacturers, equipment suppliers and independent inventors filed numerous similar patents, focusing sometimes on mechanical, sometimes on hydraulic or pneumatic correctors.

Nothing in the document mentions Citroën, Paul Magès or the future DS: this is a competitor's patent, kept in the Magès collection for technological monitoring purposes.

Archivist's perspective

The presence of this Daimler-Benz patent in Paul Magès' archives suggests that it was part of the industrial monitoring documentation that the engineer or his team consulted to situate their own work on hydropneumatic suspension in relation to the international state of the art.

The visible handwritten annotations (circled numbers, small circles in the margin, mention "7c Pb 159") probably testify to an internal filing or tracking system, no doubt to compare the ride height correction solutions proposed by Daimler-Benz with those studied at Citroën p. 14, 16-20.

This document is part of a larger series of suspension patents kept in the same file, such as the German Fox & Rice patent for General Motors on bellows air suspension or the Deveson patent on rotating shaft suspension, which confirms the hypothesis of a methodical constitution of a comparative collection on height correctors, probably useful to Magès to refine the originality of his own system.