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automotive steering[¦ȯd·ə¦mōd·iv ′stir·iŋ]
The means by which a motor vehicle is controlled about the vertical axis. It allows the driver to control the course of vehicle travel by turning the steering wheel, which turns the input shaft in the steering gear. The steering system has three major components: (1) the steering wheel and attached shaft in the steering column which transmit the driver's movement to the steering gear; (2) the steering gear that increases the mechanical advantage while changing the rotary motion of the steering wheel to linear motion; and (3) the steering linkage (including the tie rod and tie-rod ends) that carries the linear motion to the steering-knuckle arms. See Mechanical advantage
When the only energy source for the steering system is the force that the driver applies to the steering wheel, the vehicle has manual steering. When the driver's effort is assisted by hydraulic pressure from an electric or engine-driven pump, or by an electric motor, the vehicle has power-assisted steering, commonly known as power steering. Power steering allows manual steering to always be available, even if the engine is not running or the power-assist system fails.
Two types of automotive steering gears are rack-and-pinion and recirculating-ball. In a rack-and-pinion steering gear (see illustration), a tubular housing contains the toothed rack and a pinion gear. The housing is mounted rigidly to the vehicle body or frame to take the reaction to the steering effort. The pinion gear is attached to the lower end of the steering shaft, and meshes with rack teeth. Tie rods connect the ends of the rack to the steering-knuckle arms at the wheels. As the steering wheel turns, the pinion gear moves the rack right or left. This moves the tie rods and steering-knuckle arms, which turn the wheels in or out for steering.
In a recirculating-ball steering gear, a worm gear is attached to the lower end of the steering shaft. The worm gear turns inside a ball nut which rides on a set of recirculating ball bearings. These ball bearings roll in the grooves in the worm and inside the ball nut. Gear teeth on one outside flat of the ball nut mesh with a sector of teeth on the output or sector shaft to which the pitman arm is attached. As the steering wheel is turned, the rotary motion of the worm gear causes the ball nut to move up or down, forcing the sector shaft and pitman arm to rotate. This action moves the steering linkage to the right or left, turning the front wheels in or out for steering. See Antifriction bearing, Gear