About the Citroën Hydraulic System
The principles of hydraulics have been present in automotive design since the first brake system distributed pressure to each wheel by means of compressing fluid rather than pulling cables or mechanical linkages. Hydraulic systems were further used in similar ways such as operating clutch mechanisms, and in new ways such as hydraulically dampened shock absorbers, power assisted steering, and automatic transmissions.
The designers of the Citroën DS19 set out to use hydraulics in an all new way. Rather than have a number of independent hydraulic systems, each with its own fluid type, reservoir and pumping mechanism, the DS19 would have one master hydraulic system that would feed a universal fluid to specialized subsystems. This would simplify the design and create a more unified automobile.
The master hydraulic system was kept at a constant pressure, fed by a pump that was powered by the engine itself by means of a belt (the way a conventional power steering unit is powered). Hydraulic pressure was distributed to the various subsystems as needed, and would always return to a common reservoir.
The considerable amount of pressure that the engine was capable of generating gave the DS19 designers considerable creative latitude. They decided that not only would the hydraulic system dampen the suspension, but it would actually suspend the vehicle as well. Rather than employing springs or torsion bars, the designers of the DS19 made the hydraulic shocks "load-bearing." This would provide an incredibly smooth ride, and would allow certain functionality that would be impossible with conventional suspension methods. By regulating the volume of fluid distributed to the load-bearing shocks, it was possible to adjust the height at which the vehicle was suspended. By using the position of the suspension arms relative to the body as the regulating devise, it was possible for the vehicle to automatically level itself when exposed to an uneven load. By simply providing a control mechanism that effected an adjustment of the height regulation device, the overall riding height of the vehicle could be set to various levels.
The designers of the DS19 redefined the automotive hydraulic paradigm. Beyond changing the way that the hydraulic systems were implemented, they came up with entirely new ways of using hydraulics, and were able to do things that had never been done before.