How does steering really work?
It never seems like it takes much movement of your hand on the steering wheel to move such a large and heavy vehicle, does it? The steering system converts the rotation of the wheel into a swiveling movement of the road wheels in a way that the steering wheel rims turn a long way, only to move your wheels a short way. Simple, yet complex!
As an example, the rim of a 15-inch diameter steering wheel moving four full turns from full left lock to full right lock equates to travelling almost 16 feet. As it translates to the road wheels, however, these move a distance of only a bit more than 12 inches. The effort of steering transfers to the wheels through a system of pivoted joints. These are designed to let the wheels move up and down in conjunction with the suspension without altering the steering angle. This also makes sure that when cornering, the inner front wheel (which has to travel around a tighter curve than the outer one) can become more sharply angled.
There are three steering systems you will most commonly see in vehicles today:
- Rack-and-pinion system: at the base of the steering column rests a small pinion, or a gear wheel, within a housing. Its teeth mesh with another straight row of teeth on a rack, or a long transverse bar. Turning the pinion causes the rack to move from side to side, and the ends of the rack are joined to the road wheels via track rods. This is a simple system with very few moving parts to worry about replacing or becoming worn down, which equates to precise action.
- Steering-box system: at the base of the steering column with this system lies a worm gear inside a box. A worm is a threaded cylinder that looks like a short bolt. If you think about turning a bolt with a nut on it, the nut would move along the bolt. In the same manner, turning the worm moves anything fitted onto its thread. Based on what design is used, the moving part could be a sector, a peg, or a roller connected to a fork or a large nut. The worm moves a drop-arm linked by a track rod to a steering arm, which in turn moves the nearest front wheel. Also, a central track rod reaches to the other side of the car where it links to the other front wheel via another track rod and steering arm. A pivoted idler arm holds the far end of the central track, keeping it level. This system features a lot of moving parts, so it’s not as precise as the rack system and bears more room for parts wearing down or needing to be replaced.
- Power-assisted steering: On heavier cars, the steering can be equally heavy or be inconveniently low geared, meaning the steering wheel requires lots of turns from lock point to lock point. This proves troublesome when parking in confined spaces or making sharper turns, but power-assisted steering alleviates this issue. The engine drives a pump that supplies oil under high pressure to the rack or steering box. These valves open when the driver turns the wheel, allowing oil into the cylinder, and also works a piston that will push the steering in the right direction. When the driver stops turning the wheel, the valve shuts, ceasing the action of the piston. This only affects the steering motion—the steering wheel is still linked to the road wheels like usual, so if the power fails, the driver can still steer the car, however it will feel much more difficult to do so.
Being knowledgeable about your steering mechanisms and maintenance will guarantee your safety on the road.