Rack and Pinion
Most cars use a rack-and-pinion steering system in which the steering wheel turns a steering shaft that is connected to a pinion gear. This gear moves a steering rack left and right. The rack has two arms attached to it called tie rods, which connect to the steering arm and steer the wheels.
Recirculating-ball steering, often found on larger vehicles, has a design much like a nut and bolt. The bolt is a worm gear, which is attached to the steering shaft. But unlike a bolt, when the worm gear turns, it remains stationary. The nut, or ball nut rack, is a threaded block that moves forward and backward. The ball nut rack is connected to a pitman arm, which moves tie rods to turn the front wheels. Between the threaded block of the ball nut rack and the worm gear are little steel balls. They recirculate to reduce friction and wear, which removes "slop" from the steering.
The power steering system uses an additional power source to provide steering assistance when the driver turns the steering wheel. Power steering was introduced on commercial vehicles in the early 1950s and nearly all modern vehicles use it today. Power steering comes in two forms: hydraulic and electronic.
Hydraulic systems use a drive belt or an electric motor to operate a power steering pump. The pump provides the hydraulic pressure needed to assist the steering system. The pressure is then converted into mechanical force in the steering gear or rack and pinion (depending on the vehicle). When the driver turns the steering wheel, the pressure helps push the wheels in the desired direction.
The electronic power assist systems use an electric motor coupled to the steering gear or steering column. First introduced on hybrids, the system was designed to increase fuel mileage by eliminating the engine load created by a belt-driven hydraulic pump. It also allows for power assisted steering when the vehicle is operating in the electric-only mode. The assist motor is managed by a computer, which detects motion and torque through sensors on the steering column.