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DIRAVI
DIRAVI is the name given by Citroën to its proprietary power steering system, first seen in 1970.
DIRAVI is an acronym for "Direction à rappel asservi" literally meaning "steering with controlled return" more accurately described in English as "power steering with power assisted return". In the UK, it was marketed as VariPower and in the U.S. as SpeedFeel.
This was the first commercially available variable assist power steering arrangement, allowing the motorist power assist when parking, but recognizing that less steering assistance was needed at high speed. This feature is now spreading to mainstream vehicles, using electrical motors rather than hydraulic actuation.
Citroën engineer Paul Magès invented the system as part of its effort to engineer a practical high power, front-wheel drive car - a new type of vehicle at the time.
This DIRAVI system is an addition to the integrated Citroën hydropneumatic suspension and braking system. These all drew power from an engine-driven pump and hydraulic accumulator.
This unique Citroën power operated self centring steering system is fitted to Citroën SM, Citroën CX (most), Citroën XM (most V6 PRVs, and left-hand drive only), Maserati Quattroporte II, and Maserati Khamsin.
The steering wheel is connected to the hydraulic control unit, which contains a slide valve, the control gears and linkage, and the centring piston and cam. The steering rack pinion is connected to the hydraulic control unit through an adjuster, to allow setting of the centre point of the steering. This then drives one of the control gears, the other being driven by the steering wheel. The control linkage consists of two gears coupled with rods through ball-joints. When the gears are turned relative to each other, the rods move the slide valve, allowing fluid in or out of the rack. This moves the rack, which in turn moves its pinion, turning the control gears back to their centre position. Compare this with a conventional power steering system, which relies on the flexing of a strong spring to control the valve.
The steering rack is almost conventional. As with a normal power-assisted steering setup, there is a rack-and-pinion, and a stepped hydraulic ram with a dividing plate (the piston) in the middle. On one side of the plate, the piston area is half the area of the other, giving twice the area for the fluid to work on. Thus, with full system pressure on the small area side of the ram, and half system pressure on the large area side, the ram remains perfectly balanced and centred. This is because the lower pressure is working on a larger surface area. The smaller side of the piston is at constant hydraulic pressure, the other side only varies in pressure. NOTE: The author seems to be describing the DS power steering piston and rod, on which the piston is in the middle of the rod. The SM's steering cylinder has the piston on the end of the rod, which rod's cross-sectional area is half the area of the other side of the piston. Full hydraulic pressure is admitted to the rod side at all times while the pressure on the other side of the piston (its "head") is regulated.
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DIRAVI AI simulator
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DIRAVI
DIRAVI is the name given by Citroën to its proprietary power steering system, first seen in 1970.
DIRAVI is an acronym for "Direction à rappel asservi" literally meaning "steering with controlled return" more accurately described in English as "power steering with power assisted return". In the UK, it was marketed as VariPower and in the U.S. as SpeedFeel.
This was the first commercially available variable assist power steering arrangement, allowing the motorist power assist when parking, but recognizing that less steering assistance was needed at high speed. This feature is now spreading to mainstream vehicles, using electrical motors rather than hydraulic actuation.
Citroën engineer Paul Magès invented the system as part of its effort to engineer a practical high power, front-wheel drive car - a new type of vehicle at the time.
This DIRAVI system is an addition to the integrated Citroën hydropneumatic suspension and braking system. These all drew power from an engine-driven pump and hydraulic accumulator.
This unique Citroën power operated self centring steering system is fitted to Citroën SM, Citroën CX (most), Citroën XM (most V6 PRVs, and left-hand drive only), Maserati Quattroporte II, and Maserati Khamsin.
The steering wheel is connected to the hydraulic control unit, which contains a slide valve, the control gears and linkage, and the centring piston and cam. The steering rack pinion is connected to the hydraulic control unit through an adjuster, to allow setting of the centre point of the steering. This then drives one of the control gears, the other being driven by the steering wheel. The control linkage consists of two gears coupled with rods through ball-joints. When the gears are turned relative to each other, the rods move the slide valve, allowing fluid in or out of the rack. This moves the rack, which in turn moves its pinion, turning the control gears back to their centre position. Compare this with a conventional power steering system, which relies on the flexing of a strong spring to control the valve.
The steering rack is almost conventional. As with a normal power-assisted steering setup, there is a rack-and-pinion, and a stepped hydraulic ram with a dividing plate (the piston) in the middle. On one side of the plate, the piston area is half the area of the other, giving twice the area for the fluid to work on. Thus, with full system pressure on the small area side of the ram, and half system pressure on the large area side, the ram remains perfectly balanced and centred. This is because the lower pressure is working on a larger surface area. The smaller side of the piston is at constant hydraulic pressure, the other side only varies in pressure. NOTE: The author seems to be describing the DS power steering piston and rod, on which the piston is in the middle of the rod. The SM's steering cylinder has the piston on the end of the rod, which rod's cross-sectional area is half the area of the other side of the piston. Full hydraulic pressure is admitted to the rod side at all times while the pressure on the other side of the piston (its "head") is regulated.