In modern automobiles, gearboxes are used in the steering system to increase the manually applied torque. Until now, worm gears have dominated, as this was the only way to achieve the required reduction ratio in a small installation space. The disadvantages of worm gears are, on the one hand, the crossing axis transverse to the steering rod axis and, on the other hand, the fact that larger reduction ratios cannot be reversed by hand. Furthermore, the efficiency of worm gears is unfavorable due to the high proportion of sliding friction. One advantage, however, is the low noise level. Above a reduction ratio of around i=20:1, the manual backdriving torque increases exorbitantly with worm gears. Furthermore, the gears must be absolutely backlash-free to enable precise steering.

If spur gears are used instead of worm gears, the required reduction ratio can be achieved with a high torque and given installation space. A new, patented development shows that better steering gears are possible with spur gears. The Maul design office has developed an Evoloid steering gear with which significantly larger reduction ratios are possible and greater torques can be generated for steering assistance due to the increase in module size.

With correctly designed gearing, spur gearboxes can be easily turned back compared to worm gearboxes up to the highest reduction ratios. If the gearing is also noise-optimized and the smallest number of teeth of the drive pinion is used, the excitation frequency and thus the gearing noise is reduced; the "whirring" is eliminated. Tests with two devices in direct comparison of the gears show even better noise levels than with worm gears.

With the same installation space as worm gears in diameter, almost twice as high torques can be generated; for example, 30 Newton meters for worm gears and 50 to 60 Newton meters for Evoloid spur gears with i=20:1. If two drive pinions are combined and a reduction gear is connected upstream, this gear can also be used to generate higher torques and loads for heavy vehicle steering systems of 80 to 100 Newton meters with an overall reduction ratio of i=30:1. Single-stage transmissions of i=60:1 are also possible with a small installation space.

The gearbox and motor are arranged parallel to the steering column, which means that the entire system behind the steering wheel fits more compactly into the installation space of the steering column.

Zero backlash in the steering gear can be achieved in different ways; for example, elastic and preloaded wheels can be used. Setting a controlled or spring-loaded center distance also makes it possible to achieve absolute freedom from play over the entire service life of the steering gear. The parallel-axis design makes the gearbox housing more compact. pb