Louis Renault Patent No. 392,320 (1908): progressive hydraulic gear change

In this document

Object of the patent

The official fascicle presents patent No. 392,320 filed by Louis Renault on 15 July 1908, issued on 22 September 1908 and published on 24 November 1908, for a "Progressive hydraulic gear change with clutch and brake" p. 137. The fascicle bears a handwritten reference "Pb 4633 / 1959" and ink annotations circling Renault's name and the filing date p. 137.

General principle

"The drive shaft actuates a system of pumps. The pressurized liquid exiting the pumps is sent into a receiver system which in turn actuates the driven shaft" p. 137. The mechanism relies on a tilting swashplate (2) driven by the drive shaft (1), pistons (12) sliding in cylinders (14), and a distributor (17) equipped with mortises and filling valves (22) and safety valves (23) p. 137-138.

Operation

The text details how the inclination of the swashplate 2 varies the flow of the pumps and therefore the speed of the driven shaft: maximum obliquity = maximum flow, swashplate perpendicular to the shaft = "this is the moment of declutching" p. 138. By tilting further in the same direction, the direction of rotation of the driven shaft is reversed, allowing for reverse gear p. 138. For braking, "it suffices to put the swashplate 2 in the declutching position": the driven shaft then becomes the driver and the liquid, finding no flow, passes through the valves 23, ensuring braking p. 138.

Automatic control

A described variant provides for an automatic control: the pressure of the liquid acts on a piston (25) connected to the drive shaft, modifying the inclination of the swashplate according to the resisting force, which automatically varies the gear ratio p. 138-139. A sleeve (29) however allows for the manual control necessary for reverse gear, "which cannot be done automatically" p. 139. The text also refers to an earlier Renault patent, No. 385,751 of 30 December 1907, for a compatible automatic direct drive system p. 139.

The final summary p. 139 synthesizes the invention: a tilting plate driving pumps connected to an identical receiver system, allowing for variable speed, reverse gear, declutching and braking by a simple change of inclination. The document is signed "Louis RENAULT, by proxy: Georges Boju" p. 139. The single plate p. 140 illustrates eight numbered figures (Fig. 1 to Fig. 8) showing cross-sections of the mechanism.

Context

This patent belongs to the long history, largely preceding Citroën, of research into progressive hydraulic transmission — the ambition to replace dog-clutch gearboxes with a continuous system. Louis Renault, founder of the Renault factories, filed numerous patents in the first decades of the automobile.

This document does not originate from the inventive activity of Paul Magès himself: it is a historical fascicle kept in his collection, probably as a technical reference and patent watch, within the framework of his own work on hydrostatic transmission conducted at Citroën from the 1960s onwards.

Archivist's perspective

The presence of this 1908 patent in the Magès archives is revealing: it suggests that he likely studied the historical precedents of progressive hydraulic transmission before, or during, the development of his own systems. The handwritten reference "Pb 4633 / 1959" p. 137 suggests that the document was consulted or filed as early as the late 1950s, several years before the most documented developments of hydrostatic transmission at Citroën, as can be seen in the P. Magès' presentation on hydrostatic transmission or the Handwritten notes "Presentation T.H. 50 CV".

The principle described — axial piston pumps and tilting swashplate — anticipates, by a century, the architectures that will be found studied in the technical plates of the GS hydrostatic transmission. This patent thus constitutes a valuable piece of technical context, at the crossroads of automotive history and Magès' work as an engineer.