The direction of motion of a motor vehicle is controlled by a steering system.
A basic steering system has 3 main parts: A steering box connected to the steering wheel. The linkage connecting the steering box to the wheel assemblies at the front wheels. And front suspension parts to let the wheel assemblies pivot.
When the driver turns the steering wheel, a shaft from the steering column turns a steering gear. The steering gear moves tie rods that connect to the front wheels. The tie rods move the front wheels to turn the vehicle right or left.
There are 2 basic types of steering boxes - those with rack-and-pinion gearing, and those with worm gearing. In both cases, the gearing in the steering box makes it easier for the driver to turn the steering wheel, and hence, the wheels.
A rack-and-pinion steering system has a steering wheel, a main-shaft, universal joints, and an intermediate shaft. When the steering is turned, movement is transferred by the shafts to the pinion. The pinion is meshed with the teeth of the rack, so pinion rotation moves the rack from side to side. This type of steering is used on passenger vehicles because it is light, and direct.
This steering system has worm gearing. It provides a gear reduction, and a 90 degree change in direction. It has more parts and joints than the rack type, but it is more robust, and may be used on heavier vehicles.
To allow heavy transport vehicles to carry extra weight, two steering axles may be used. They’re connected by a link to a common steering box. These vehicles are called tandem, or twin-steered vehicles.
Some passenger vehicles also steer the rear wheels slightly. This gives improved manoeuvrability. The system is known as 4-wheel steering.
It can be controlled mechanically, through a direct connection, between the front and rear steering boxes.
Or it can be computer-controlled.
With heavier vehicles, increased use of front-wheel-drive, and wider, low-profile tyres, more steering effort is needed, so power steering is used.
An engine-driven hydraulic pump provides pressure that helps the driver steer the vehicle. The power steering system is designed so that the vehicle can still be controlled, even if the engine or the power steering system, fails.