Equipment Specs

Rack-and-pinion Steering

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Mechanical Features and Designs
Top View of Rack and Pinion Steering System
Rack-and-pinion steering
is perhaps the most common type of steering on cars, small trucks, and sports utility vehicles. Rack-and-pinion gears use two interlocking gears (one circular and one straight) to convert rotational movement into linear movement. When used as part of a steering system, the rack (the straight gear) is connected to the wheels; the pinion (the circular gear) is attached to the steering wheel. The rack-and-pinion gearset also provides gear reduction, making it easier to turn the vehicle’s wheels.[1]


[edit] How it Works

A rack-and-pinion gearset is comprised of two interlocking, notched gears: a circular pinion and a straight rack. In a rack-and-pinion steering system, the rack-and-pinion gearset is set inside a metal tube, from which each end of the rack protrudes.

The pinion is attached to the vehicle's steering shaft. A tie rod attached to each end of the rack connects the rack to the steering arm on each wheel.

When the steering wheel is turned, the pinion spins, moving the rack to the right or to the left, depending on which way you turn the wheel.

For the majority of cars, three or four revolutions of the steering wheel are required to make the car’s wheels turn from the far left to the far right.

[edit] Steering Ratio

The steering ratio is the ratio of the turn of the steering wheel (in degrees) and the turn of the wheel (in degrees). If a 360-degree revolution of a steering wheel makes the car's wheels turn 20 degrees, the steering ratio would be 360 divided by 20, or 18:1. The lower the steering ratio, the faster the wheels change direction in response to a turn of the steering wheel.

[edit] Power Steering

Power steering involves a slightly different rack-and-pinion configuration. In this case, part of the rack includes a cylinder with a piston in the middle, which is connected to the rack. A fluid line on either side of the piston supplies high-pressure fluid to the piston and forces it to move. The movement of the piston moves the rack, which provides the power assist element.

[edit] References

  1. Steering. 2008-09-30.

[edit] External Links