Power steering
[1] Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver can provide less effort to turn the steered wheels when driving at typical speeds, and considerably reduce the physical effort necessary to turn the wheels when a vehicle is stopped or moving slowly.
[2] The next power steering system was put on a Columbia 5-ton truck in 1903 where a separate electric motor was used to assist the driver in turning the front wheels.
[6][7][8] Davis moved to General Motors and refined the hydraulic-assisted power steering system, but the automaker calculated it would be too expensive to produce.
General Motors introduced the 1952 Cadillac with a power steering system using the work Davis had done for the company almost twenty years earlier.
Charles F. Hammond from Detroit filed several patents for improvements of power steering with the Canadian Intellectual Property Office in 1958.
[10][11][12] Starting in the mid-1950s American manufacturers offered the technology as optional or standard equipment while it is widely offered internationally on modern vehicles, owing to the trends toward front-wheel drive, greater vehicle mass, reduced assembly line production costs, and wider tires, which all increase the required steering effort.
A study in 1999 on the perceptual fidelity of steering force feedback, found that ordinary real-world truck and car drivers naturally expect an increase in feedback torque as speed increases, and for this reason early forms of power steering, which lacked such effect, were met with disapproval.
Because this would be undesirable, a restricting orifice and flow-control valve direct some of the pump's output back to the hydraulic reservoir at high engine speeds.
Each vehicle owner's manual gives instructions for inspection of fluid levels and regular maintenance of the power steering system.
Some modern systems also include an electronic control valve to reduce the hydraulic supply pressure as the vehicle's speed increases; this is variable-assist power steering.
[18][19] In 1988, the Subaru XT6 was fitted with a unique Cybrid adaptive electro-hydraulic steering system that changed the level of assistance based on the vehicle's speed.
[20] Electro-hydraulic systems can be found in some cars by Ford, Volkswagen, Audi, Peugeot, Citroën, SEAT, Škoda, Suzuki, Opel, MINI, Toyota, Honda, and Mazda.
Engineers can therefore tailor steering-gear response to variable-rate and variable-damping suspension systems, optimizing ride, handling, and steering for each vehicle.
[23] Electric systems have an advantage in fuel efficiency because there is no belt-driven hydraulic pump constantly running, whether assistance is required or not, and this is a major reason for their introduction.
By incorporating electronic stability control electric power steering systems can instantly vary torque assist levels to aid the driver in corrective maneuvers.
[25] In 1988, Koyo Seiko (currently JTEKT) and NSK co-developed a column system exclusively for minicars sold only in the domestic market of Japan.
In the year 1990, a direct full control system of a rack assist without a clutch was put into practical use in the Honda NSX (initially installed in automatics only).
These last are more accurately called non-linear types (e.g. Direct-Steer offered by Mercedes-Benz); a plot of steering-wheel position versus axle steering angle is progressively curved (and symmetrical).
