Power steering was once considered an optional luxury, but changes in automobile configurations made this feature essential to most drivers. Steering originally depended only on the driver's muscular exertions, but cars became heavier as equipment was added and tires became softer to cushion the ride. The softer tires hugged the road, but friction also increased so more force was needed especially during turning. The passenger compartment and the engine moved forward as improvements were made to road handling and comfort, but this shifted more of the load to the front wheels. Front-wheel drive also added efficiencies to car operations but complicated the average driver's ability to steer.
At first, steering was adapted to these changes by mechanical improvements to the bearings, linkages to the front wheels, and the gears that transmit the movement of the steering wheel to the front wheels. The "average" driver was changing too, and the increase in the number of women drivers also pushed the industry to provide steering assistance.
Power-assisted steering was actually used with some steam-powered vehicles in the early 1800s. It was rediscovered by the military and adapted to heavy trucks and military vehicles in the 1930s, but it was not revived and applied to passenger cars with internal combustion engines until the 1950s. During power-assisted steering, as the driver applies turning moment or torque to the steering wheel, a hydraulic device driven by the engine amplifies this torque at the wheels to overcome the forces of weight and friction. Chrysler introduced power steering by adapting hydraulic power cylinders and jacks that had been developed by the aircraft industry. A pressure-sensitive valve responds to steering force by supplying fluid under pressure from a pump to the jack cylinder connected to the chassis. As the car begins to move and turn, less steering force is needed, the fluid supply and resulting boost is reduced, the steering wheel returns to the forward direction, and the process reverses until the wheels are moving straight ahead.
Other power steering systems use track rods connected to the control valve or, instead of a hydraulic jack, a ball nut inside the steering gear casing forms a similar piston inside a cylinder. Improvements to power steering allow the system to recognize the relationship between speed and the need for powered assistance. The need for power steering diminishes with increased speed, but the system remains sensitive to flat tires or other sudden slow-downs and keeps the wheels straight despite these apparently abrupt turns.
This is the complete article, containing 410 words
(approx. 1 page at 300 words per page).
