DIRAVI
| Company type | Technology |
|---|---|
| Industry | Automotive |
| Founded | 1970 |
| Founder | Paul Magès |
| Products | Power steering system |
| Parent | Citroën |
DIRAVI is Citroën’s exclusive power steering technology, launched in 1970.
Name
The acronym DIRAVI derives from "Direction à rappel asservi," which translates to "steering with controlled return," or more specifically, "power steering featuring power-assisted return." This system was branded as VariPower in the United Kingdom and as SpeedFeel in the United States.
Purpose
DIRAVI was pioneering as the initial commercially introduced power steering system that provided variable assistance—delivering strong power aid at low speeds (such as during parking maneuvers) and diminishing assistance as speed increased. This principle has since been adopted widely, with many modern vehicles employing electric motor-driven systems instead of hydraulic ones.
Conceived by Citroën engineer Paul Magès to accommodate practical high-powered, front-wheel drive automobiles, DIRAVI operates in conjunction with Citroën’s hydropneumatic suspension and braking systems. It is powered by a hydraulic pump driven by the engine and supported by an accumulator.
This steering system was fitted to vehicles including the Citroën SM, most versions of the Citroën CX and Citroën XM (notably V6 PRV, left-hand drive models), along with the Maserati Quattroporte II and Maserati Khamsin.
How it works
The steering wheel links to a hydraulic control assembly that contains a slide valve, control gears, connecting linkages, and a centring piston equipped with a cam. The rack-and-pinion mechanism incorporates a stepped hydraulic ram balanced via different piston areas and regulated fluid pressures to maintain centring force.
Unlike traditional power steering systems that depend on spring tension, DIRAVI hydraulically locks the steering against road feedback within its operational limits. The level of assistance remains consistent regardless of speed; however, a pressure-regulated piston acting on a cam adjusts both steering effort and centring force according to vehicle velocity. This pressure is governed by a centrifugal regulator connected to the gearbox output shaft, increasing progressively up to approximately 120 mph.
In the event of hydraulic pressure loss, the system defaults to a mechanical backup mode characterized by considerable play and increased steering effort—intended solely for emergency use.
To avoid excessive control sensitivity at higher speeds, the centring cam modulates self-centring force from roughly 290 psi at low speeds up to about 800 psi near 80 km/h, enhancing stiffness without overly restricting steering responsiveness.
Features
- Entirely hydraulic operation with no direct mechanical connection between the steering wheel shaft and steering pinion during normal use; it hydrostatically locks wheel position similarly to a bulldozer hydraulic ram, isolating road disturbances from the steering input.
- Power-driven rather than relying on traditional power-assisted mechanisms.
- Quickly self-centers to neutral position whenever the engine is running, even when stationary.
- Simulated steering feel adapts according to vehicle speed and degree of wheel turn.
- Powered by a regulated high-pressure hydraulic pump that also supplies brakes and suspension systems.
- The rack-and-pinion assembly primarily serves as a feedback mechanism; its rack functions as a double-acting hydraulic ram capable of full steering control if hydraulic pressure is lost.
- A priority valve for hydraulic power ensures appropriate fluid distribution among circuits.
- In case of hydraulic failure, loss of function occurs first in steering, followed by suspension, then braking systems.
Advantages
- Absence of steering kickback—uneven road surfaces do not influence steering inputs or wheel direction because the feedback is artificially generated and independent of actual road forces.
- Extremely low physical exertion—lock-to-lock steering can be accomplished with minimal effort, even with a single finger when the vehicle is stationary (SM variant).
- Rapid response—lock-to-lock rotation takes 2.0 turns in the SM version and 2.5 turns in the CX setup.
- Capable of maintaining a straight path on roads with consistent camber without requiring driver intervention.
- Enhances handling in front-heavy vehicles by delivering precise and effortless control, facilitating swift reactions at elevated speeds.
Disadvantages
- Lacks genuine feedback for the driver; the synthetic feel does not correspond to real front-wheel forces or road surface conditions.
- Feedback and kickback are destabilizing influences transmitted through the steering geometry; neutral geometry removes these forces but also eliminates natural tactile sensation.
- Certain models such as DS, ID, GS, and SM employ neutral steering geometry (zero scrub radius), allowing the wheel to pivot exactly around a vertical axis—a configuration uncommon in automotive engineering.
- Neutral geometry permits normal steering and braking even after a front tire failure; however, these systems do not provide inherent tactile feedback once the vehicle is in motion.
- Diravi introduces an artificial self-centering force to offset the lack of natural feedback and hydrostatically locks the wheels at the selected angle, preventing external forces from altering steering position.
- Enables effortless parking and precise handling at speeds exceeding 200 km/h in heavy front-wheel-drive automobiles.
- The artificial feel is designed to offer a consistent steering sensation across various speeds rather than transitioning from soft to firm feedback.
- The CX model features non-neutral geometry (12° caster) which enhances braking stability but would produce noticeable feedback without Diravi’s hydrostatic locking mechanism.
- Diravi conceals the effects of non-neutral geometry during tire blowouts by locking the rack at the chosen steering angle.
- Drivers must depend on visual indicators to judge approaching limits of road grip due to the absence of mechanical feedback.
- Requires acclimatization by drivers; beginners might perceive Diravi as overly sensitive and too quick in response.
- The swift self-centering action prevents hands-free cornering.
- Because there is no rigid mechanical linkage, hydraulic system failure can diminish control precision; however, the SM model incorporates a backup mechanical connection that allows for heavy yet safe steering under failure conditions.
- Achieving neutral geometry is challenging with outboard brakes; thus, DS, ID, and GS utilize inboard brakes, SM combines inboard brakes with Diravi, whereas CX employs Diravi with outboard brakes but with less neutral geometry.