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How Do Steering Systems Work?

By: Kevin Watson MSc - Updated: 4 Aug 2010 | comments*Discuss
 
Steering System Car Rack-and-pinion

A car’s steering system is not as straightforward as it might first appear. When a car turns, for instance, the front wheels don’t point the same way. This difference is vital for smooth driving. The outer wheel on a turn has to track a larger circle than the inner wheel. The front wheel on the outside therefore turns at a less acute angle than the inner.

Another way of looking at this is to take a compass and draw two circles, one inside the other. The inside wheel of a turning car tracks the inner circle; the outside wheel tracks the outer.

Now mark the position of two front wheels on the circles. Do this so that the marks are the same length and balanced on the edge of the circle. Also set the outside wheel further back than the inside wheel. This recreates the actual position of the front wheels of a car making a turn. The two marks that represent the wheels are pointing in different directions. A car’s steering system has to make an allowance for this difference every time a driver turns.

Rack-and-Pinion

There are two common types of car steering system: rack-and-pinion and recirculating ball.

With rack-and-pinion, the steering wheel connects to a steering shaft and then to a pinion. The pinion is a wheel with a series of projections on its edge. These projections engage with the serrations on a straight piece of metal tube. This tube is the rack.

When a driver turns the steering wheel, the pinion pushes the rack to the left or right. Tie rods at the ends of the rack transfer this movement to steering arms. These arms connect to the spindles on the front wheels.

The way the pinion and rack work together creates a gear reduction. The gear reduction ensures that a driver can turn the front wheels with relative ease.

Recirculating Ball

A recirculating ball steering system appears mainly on lorries and some SUVs. The main difference to a rack-and-pinion system is the use of a worm gear. A worm gear has a revolving cylinder with a screw-like thread.

The driver turns the steering wheel. This movement revolves the worm gear. The worm gear then causes a block to move a serrated gear. The gear moves a piece of metal rod called a Pitman Arm.

The Pitman Arm connects to a track rod. In a similar fashion to rack-and pinion steering, the track rod has tie rods at each end. These connect to the wheels’ steering arms. The name ‘recirculating ball’ comes from the ball bearings that are in the block that the worm gear turns. The ball bearings recirculate around the inside of the block.

Power Steering

Power steering appears on most new cars. Manufacturers use it for rack-and-pinion and recirculating ball systems. The principle of power steering is similar for both.

Essentially, a power steering system has a rotary-vane pump. A belt from the car’s engine supplies the power to the pump. In turn, the pump gives the steering wheel the hydraulic power that makes turning a car much easier than a traditional system.

The power steering mechanism only comes in use when a driver puts pressure on the steering wheel. This occurs during a turn. When a car travels in a straight line, the pump isn’t active.

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