DIRAVI

DIRAVI is the name Citroën gave to a proprietary hydraulic steering system first introduced in 1970. The acronym comes from the French expression “Direction à rappel asservi,” commonly rendered as steering with controlled return. In practical terms, it is a power-operated steering arrangement with powered self-centering and a steering feel that becomes progressively heavier as vehicle speed rises. The system was marketed as VariPower in the United Kingdom and as SpeedFeel in the United States. The technology was developed by Citroën engineer Paul Magès during the company’s effort to make high-powered, front-wheel-drive cars manageable and precise. It appeared first on the Citroën SM, a technically ambitious grand touring car, and was subsequently fitted to most Citroën CX models and many Citroën XM V6 models. It was also used on the Maserati Quattroporte II and Maserati Khamsin, reflecting the connection between Citroën’s advanced hydraulic technology and Maserati vehicles produced during the period when Citroën controlled Maserati. Unlike conventional power-assisted steering, which normally retains a direct mechanical connection and supplements the driver’s effort, DIRAVI is fundamentally hydrostatic. During normal operation, hydraulic pressure controls the steering rack and isolates the steering wheel from most disturbances transmitted by the road. The steering wheel therefore does not receive conventional kickback from potholes, ruts, or tire disturbances. A feedback mechanism connected to the rack provides steering-position information to the hydraulic control unit, while a speed-sensitive centering mechanism supplies an artificial steering feel. The system draws hydraulic power from the same high-pressure architecture used by Citroën’s hydropneumatic suspension and braking systems. A pump and accumulator provide pressure, and valves prioritize hydraulic availability between the vehicle’s steering, suspension, and braking functions. At low speed, the steering remains extremely light, allowing the driver to turn the wheel with minimal effort while parking. As speed increases, pressure acting on a centering piston and heart-shaped cam increases the self-centering force. This makes the steering progressively more resistant to rapid or excessive inputs while preserving the system’s unusually quick response. DIRAVI was notable for making large, heavy, front-wheel-drive cars easy to maneuver. On the SM, the steering could move from lock to lock in about two turns, while the CX used approximately two and a half turns. The system’s rapid response and absence of road shock were distinctive features, but they also required driver familiarization. Drivers accustomed to conventional steering could find the steering overly light, sensitive, and lacking in natural road feedback. The rapid return to center also meant that the driver had to maintain control of the wheel through curves. A hydraulic failure did not leave the steering entirely without a mechanical fallback. The rack could be moved mechanically through a split-shaft arrangement, but this emergency mode involved substantial play and very heavy effort. The steering circuit was designed to be sacrificed before the suspension and brakes when hydraulic pressure was lost, so unpowered steering was intended only to guide the vehicle to a safe stopping place. DIRAVI’s reliance on the broader Citroën hydraulic system was therefore both a technical strength and a maintenance consideration. DIRAVI was an early commercially deployed example of variable-assist steering. Modern vehicles commonly achieve similar speed-sensitive assistance with electronically controlled electric motors, but DIRAVI accomplished the effect through hydraulic pressure, mechanical governors, gearbox-related speed signals, and a deliberately engineered centering mechanism. Its importance lies less in being a standalone consumer product than in demonstrating an alternative steering philosophy: steering effort and return force could be actively generated rather than merely reduced through conventional assistance.

DIRAVI emerged from Citroën’s broader program of hydraulic and front-wheel-drive innovation. Citroën engineer Paul Magès developed the system as the company sought to make a powerful, front-heavy, front-wheel-drive vehicle practical to drive. The resulting design departed from the usual model of power assistance. Instead of simply reducing the effort required to move a mechanically connected steering system, DIRAVI used hydraulic control as the primary means of steering during normal operation. The system was introduced in 1970 on the Citroën SM. The SM combined Citroën’s hydropneumatic suspension and braking technologies with a high-performance drivetrain, creating unusual demands for steering control. DIRAVI addressed those demands with extremely light parking effort, rapid steering response, and a mechanism that automatically returned the wheel toward center. It also reduced the transmission of road disturbances to the steering wheel, a characteristic that distinguished the SM from cars with conventional steering arrangements. DIRAVI was integrated into Citroën’s centralized high-pressure hydraulic system. The same general hydraulic infrastructure supported steering, suspension, and braking. A pump and accumulator supplied pressure, while valves managed hydraulic priority. Within the steering unit, the steering wheel operated a hydraulic control assembly containing a slide valve, gears, linkages, and a centering piston and cam. Relative movement between the steering input and rack-position feedback opened the appropriate hydraulic passages and moved the rack. The steering feel was not generated primarily by direct mechanical reaction from the front wheels. Instead, a speed-related hydraulic pressure acted on a centering piston and heart-shaped cam. At low speeds this produced light assistance and modest self-centering. As speed rose, the centering force increased, creating a heavier and more stable steering sensation. Speed information could be derived through a centrifugal governor driven by the gearbox on manual-transmission vehicles; automatic-transmission applications used transmission governor pressure. The arrangement gave the driver a changing steering resistance without abandoning the system’s hydraulic operating principle. After the SM, DIRAVI was installed in most Citroën CX versions and in many V6 versions of the Citroën XM, with the XM applications limited to left-hand-drive vehicles according to the cited reference material. The technology also crossed into Maserati applications, notably the Quattroporte II and Khamsin. In the United Kingdom it was marketed under the VariPower name, while the United States used the SpeedFeel designation. These market names reflected the same underlying Citroën technology rather than separate steering architectures. DIRAVI offered several technical advantages. It made parking exceptionally easy, responded rapidly to small steering inputs, and largely prevented road shocks from disturbing the steering wheel. It could also maintain a straight-ahead tendency on a constant-camber road under suitable conditions. However, the artificial nature of its steering feedback could make the system unfamiliar to drivers. The steering was sensitive, the wheel returned quickly toward center, and the driver received little direct information about tire forces or road texture. The system’s safety behavior was closely tied to the hydraulic network. In the event of a loss of hydraulic pressure, normal power operation ceased and the rack could be moved through a mechanical backup path. That backup involved considerable free play and very heavy steering effort, making it suitable only for moving the vehicle to a safe location. Hydraulic prioritization was designed so that steering assistance was lost before suspension and braking functions. This arrangement illustrates both the sophistication and the complexity of DIRAVI. Although DIRAVI did not become a universal industry standard, it anticipated the later spread of variable-assist steering. Contemporary systems generally use electronic controls and electric motors rather than Citroën’s high-pressure hydraulic architecture. DIRAVI remains historically significant as one of the earliest commercially available variable-assist steering systems and as an example of Citroën’s distinctive approach to vehicle engineering.

• 1970

  DIRAVI introduced on the Citroën SM

  [1]DIRAVIen.wikipedia.org

  Citroën introduced its fully hydraulic, speed-sensitive steering system on the Citroën SM, combining light low-speed steering with powered self-centering and increasing resistance at higher speeds.

• Adopted for the Citroën CX

  [1]DIRAVIen.wikipedia.org

  DIRAVI was fitted to most Citroën CX models, extending the technology from Citroën’s grand tourer to its large executive and family-car range.

• Adopted for selected Citroën XM V6 models

  [1]DIRAVIen.wikipedia.org

  Many V6-powered Citroën XM models received DIRAVI, with the cited reference identifying the application as limited to left-hand-drive cars.

• Used in Maserati applications

  [1]DIRAVIen.wikipedia.org

  The system was also installed in the Maserati Quattroporte II and Maserati Khamsin.

An advanced, fully hydraulic steering technology positioned around effortless low-speed maneuvering, rapid self-centering, high-speed steering resistance, and isolation from road shock.

• Automotive steering system · 1970

  DIRAVI

  Citroën’s fully hydraulic steering system with speed-sensitive self-centering. During normal operation, hydraulic pressure performs the steering work and isolates the steering wheel from most road disturbances. A hydraulic control unit, rack feedback, and a pressure-loaded cam mechanism create the system’s rapid response and changing steering resistance. In the event of pressure loss, a heavy mechanical fallback allows limited steering control.

1. 1DIRAVIen.wikipedia.org