Saturday, July 25, 2009

Car Steering System

An automobile steering system allows the driver to control the vehicle’s direction. Rotation of the steering wheel is translated, through gearing and a network of rods and joints (the steering linkage), into right or left movement of the car’s front wheels.

There are two basic types of steering systems, rack and pinion, and worm and roller (or worm and key). The rack and pinion is the simples, and the one most commonly used in modern cars. In rack and pinion linkage, the steering shaft, connected at one end to the steering wheel, has a pinion gear at its opposite end. The gear meshes with threads in a steering rack, which is mounted across the car and is connected by the rods to the front wheels. The steering wheel turns the steering shaft, the pinion gear on the shaft’s end moves the steering rack to the right or left and thus moves the wheels. Rack and pinion systems use how few moving parts but perform precisely and efficiently.

In worm and roller systems the steering shaft ends in a gearbox, which is connected to the steering linkage by a special rod called a Pitman arm. On the left side of the car, an idler arm is mounted parallel to the right mounted Pitman arm. The arms are connected by a relay rod. Inserted into the relay rod are tie rods connecting it to the two front wheels, and short tire-steering arms that are joined to the tire rods by ball joints. Inside the gearbox the worm – a spiral threaded gear on the end of the steering shaft meshes at right angles with a roller, or a key. (A roller is a threaded gear; a key is a device with a single tooth that engages the threads of the worm gear.) As the steering wheel is turned, the roller or key moves right or left along the worm gear, swiveling the Pitman arm.

The recirculation ball steering gear resembles the worm and roller mechanism, except that the gears ride on a number of ball bearings, which act as lubricants, reducing gear friction.

Many modern vehicles have power assisted steering, which uses hydraulic pressure to reduce the effort needed to steer. In the most common system, a power steering pump, connected by a belt to the engine, sends high pressure fluid to the steering gearbox, where it aids in moving the gear.

Innoactive 4 wheel steering (4WS) is now available in the modes, either all 4 wheels turn in the same direction, or front and rear wheels turn in opposite directions. Both systems are said to produce the same effects; parking is far easier, and high speed maneuvers are safer because fishtailing is reduced. In either mode, 4WS is still relatively untired, but it may prove eventually to be the steering system of the future.

other article:
Automobile Racing
Automobile History

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