Operation

Operation

The innovative characteristic of this steering system lies in the difference between the maximum effort applied to the steering wheel when the car is on a bend or executing manoeuvres with high steering angles, and the minimum effort applied when the steering wheel is in the straight, or virtually straight, driving position.

Graph showing the different efforts applied with 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 offer 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 the pressure angle and modulus varying from the centre towards the ends, so the pinion engages with teeth of different pitch depending on the steering angle executed.

A more direct ratio is thus obtained when the pinion is working on the central part of the rack and a more demultiplied ratio is obtained as the pinion engages nearer the two ends of the rack during steering. This leads to higher sensitivity of the car on straight lines and greater comfort on bends and during manoeuvres.

View of the variable-ratio steering gear with schematic representation of the rack teeth and pinion.