and pinion steering
system is, in actual fact, a very simple gear
mechanism which turns the rotation
of the vehicle's steering wheel
into a linear motion which turns the wheels in one direction or the other to steer the vehicle.
As its name suggests, rack and pinion steering has two main components, the rack and the pinion.
The rack is a long rod which is situated between the two wheels which steer the vehicle. It has a set of gear teeth along its length.
The pinion is a round cog attached to one end of the vehicle's steering shaft, (the vehicle's steering wheel is attached to the other)! The pinion's gear teeth engage with those of the rack.
When one rotates the steering wheel, the rotation of the pinion causes the rack to move linearly in the direction the steering wheel was turned. The tie rods attached to the end of the rack move correspondingly, which causes the vehicles wheels to "change direction" and steer the vehicle. Easy!
As a footnote; one word I've used quite a lot here is gear: Another function of the rack and pinion steering system is to provide gearing to reduce the number of turns of the steering wheel required to turn the vehicle a particular amount. The higher the gear ratio, the lower the number of turns of the steering wheel required to go 'lock-to-lock', (i.e. to traverse the length of the steering rack). In other words, the steering system is more 'sensitive'. Many rack and pinion steering systems have a varying tooth pitch along the rack so that the sensitivity of the vehicle's steering changes according to how far away from 'dead centre' the rack has moved.