The steering column is connected to the input shaft by a flexible joint. Some manufacturers fit sensors and control units to the steering column, which provide information to steering control modules as part of an electric assisted or 4-wheel steering system.
The rack-and-pinion steering box has a pinion, connected to the steering column. This pinion runs in mesh with a rack that is connected to the steering tie rods.
With variable ratio steering, as the steering moves away from the straight-ahead position, the ratio, and therefore, the mechanical advantage, increases progressively.
Variations of worm-type steering boxes are worm-and-sector, worm-and-roller, worm-and-nut, and recirculating ball. The steering box gear ratio increases output torque, reducing the effort the driver must apply.
When a load is applied to the steering system, the torsion bar twists, causing relative movement of the inner and outer members of the rotary valve. Assistance progressively rises as the torsion bar twist increases.
Power steering pumps have a flow-control valve to vary fluid flow and system pressures. A pressure relief valve prevents excessive pressures developing when the steering is on full-lock.
Electric steering is more economical to run, and easier to package and install than conventional hydraulic power steering systems. They are also lighter and more compact than conventional hydraulic systems.
The microprocessor control unit analyzes inputs from the steering sensor as well as the vehicle's speed sensor. The sensor inputs are then compared to determine how much power assist is required.
