Dismantling-refitting (page 2 of 2)

Its innovative characteristic is that it can reduce the difference between the maximum force applied to the steering wheel when the car is on a bend or carrying out manoeuvres with tight steering angles, and the minimum force applied when the steering wheel is for example in the position for driving on a straight line.

Graph showing the different forces applicable on a constant ratio steering gear and a variable ratio steering gear.

• Constant ratio steering gear
• Variable ratio steering gear

This characteristic is obtained thanks to the particular shape of the rack teeth, which can determine variable ratios between the force applied to the steering wheel and the force transmitted to the wheels, depending on the position assumed by the rack in relation to the pinion.

The rack teeth are cut with module and pressure angle varying from the centre towards the ends, so that the pinion engages with teeth of different pitch depending on the steering angle executed.

Thus a more direct ratio is obtained when the pinion works on the central part of the rack, and a more geared-down ratio is obtained as the pinion engages nearer the two ends of the rack during turning. This offers more sensitive handling of the car on straight lines and more comfortable handling on bends and during manoeuvres.

Cross-section of the variable ratio steering gear showing a schematic representation of the rack and pinion teeth.