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Efficient newcomer attempts to steal wormgear`s crown

11 June, 2007

The German gear-motor manufacturer Zeitlauf has revived a century-old idea – the crown gearhead – to develop a range of angle gearheads which, it claims, are more efficient and longer-lasting than wormgear or bevel spur gear systems.

Crown gears consist of a cylindrical pinion (corresponding to an involute spur wheel) which interacts with a cog wheel, whose geometry varies over the width of the tooth. The teeth roll off each other with low friction, rather than sliding as happens in wormgears.

Although crown gears have been used in applications such as drive rod gearboxes, couplings and power tools, their complex tooth geometry has made them difficult and costly to apply to precision power gears.

For the past ten years, Zeitlauf has been collaborating with a group of other organisations – including RWTH Aachen University and the Swiss gear-cutting specialist Schnyder – to develop a cost-effective method for manufacturing crown gears using 21st century technologies, such as computer simulations.

Zeitlauf Etacrown cutaway

The resulting EtaCrown gearboxes (shown above in a cutaway view) operate with an efficiency in the range 85–96%. This means that their losses are up to 70% lower than those of similarly-rated worm gears, allowing smaller, cheaper motors to be used, and reducing the space needed to accommodate gearmotors by up to 30%. Unlike worm gears, the crown gears do not suffer from self-locking.

Because conventional tooth-gear gauging machines were not capable of measuring the small cogwheel geometries, Zeitlauf and its partners had to develop a special 3D gauging machine. They also produced a special gear-shaping machine to manufacture the crown gears economically in small batches.

Reductions in the range 4:1 to 113:1 are possible using one stage (delivering up to 4Nm of output torque), and up to 170:1 using two stages (up to 10Nm). Start-ups are said to be jolt-free, and noise levels low – especially if plastic gears are used.

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