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F1 Power Steering Rack
Posted on June 21, 2016
Much like the shift in road car steering, F1 steering is now power assisted, with the hydraulic power steering rack now has been standard for many years. Integrated as part of the cars high power hydraulic system, the rack is an essential part of the cars set up. Without it the current suspension geometry at the upright would be impossible to steer without power assistance. Like all F1 hydraulic solutions, the rack is a simple solution, made possible by finely engineered details.
Operated in classic racecar fashion, by a steering column acting on a rack and pinion set inside the rack’s body, the basic mechanics of F1 steering are simple. A kind of chicken and egg situation has grown up around the upright geometry with increasing offset being used to provide feedback at the cost of the mechanical effort to require to steer the car. Power steering allows the geometry and as a result the geometry becomes even more exaggerated, both sides driving each other. Now an F1 car is un-drivable without power steering and to some extent easy because of the power assistance, allowing the drivers to be of slimmer build.
The hydraulic process is also simple, a double acting piston is supplied with a pressurized hydraulic fluid to aid the rack and pinion move in either direction. The hydraulic fluid is supplied as part of the cars main hydraulic system, from a pump driven by the engine. The FIA regulatory requirement for the steering to be a simple hydro-mechanical system, means that no electronics are involved in the process, so none of the Moog electro servo valves are used. This makes metering the fluid flow and tuning the system to the driver’s demands, a tricky exercise in the detail design of the system. Perhaps in hindsight a SECU monitored electronic system would have been cheaper, than teams investing huge resources in mechanical engineering to tailor the system to each car\driver?
Moog Spool valves
Translating the drivers turn of the steering column into a precise fluid flow into the piston is the job of the spool valve. Despite being a passive mechanical part, it’s still often made by electro-servo valve supplier Moog. With movement in either direction the spool valve meters a pressurized supply of fluid to either side of the piston. To move the spool valve there needs to be a tiny amount of ‘give’ in the column to rack movement, this lost movement is translated to the spool valve and into the rack. This effect isn’t felt by the driver, such is the efficiency and accuracy of the spool valve, only a microscopic amount of movement is required.
To provide this give there are two ways to have the offset movement, in the column itself or in the rack and pinion interface.
I have a Williams F1 Steering rack, while its nearly complete the spool valve is missing, but it’s clear the system uses the column flex to provide the spool valve movement. The last section of steering column going into the rack is separate from the main steering column and a precision machined part of the rack assembly. The column shaft thins and a small angular flex is created in the shaft when steering movement is put into the system by the driver. This flex rotates a spool valve mounted around the column and this then sends proportional pressure change into the piston.
Other racks use a flexure at the point where the pinion meets the rack. Rather than a solid mounting of the pinion into the rack body, there a “W” shaped flexure, when steering effort is put into the system, the pinions moves laterally a tiny amount. This operates the spool valve which then provides the proportional fluid control.
Both systems see active use in F1, with steering racks increasingly tucked away out of sight inside the front bulkhead, it’s not possible to see which remains the more popular solution and who has what set up.
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