Efficiently “going Around The Corner” With Crown Gear Drives

If a drive power is to go “around the corner”, bevel or worm gears are widespread for the reduction of high-speed electric motors. However, you always accept disadvantages when using them.

Worm gear: Axial misalignment between the input and output shafts

In principle, worm gears have an axial offset between the input and output shafts and work with comparatively poor efficiency, so that drives often have to be dimensioned larger.

Bevel gear: limited in the reduction

Bevel gearboxes are usually geared down to a max. 5: 1 limited and therefore not the ideal choice. Their efficiencies are quite high, but their production is complex, which is reflected in the price.

Crown gearbox: sticking point calculation

If you are looking for a very economical and efficient right-angle gearbox, you should look at the crown gear technology. Crown gear units were used in technical systems centuries ago and can still be seen in historical mills today. Over time, they were then replaced by bevel gears because they were easier to calculate; the crown wheel disappeared from the market.

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Focus on energy-efficient drive technology

That changed, however, when smaller drives became the focus of efforts to achieve energy-efficient drive technology in industry. The right combination of efficient motors, gears and controls ultimately enables high energy savings even in the power range below 250 W. Since decentralized drive technology has become increasingly important due to its flexibility in mechanical and plant engineering, there are more and more such drives. Gearboxes that work with the highest possible efficiency are therefore in demand and crown gear technology can score points here.

The gearbox specialist Zeitlauf, which belongs to the EBM-Pope, recognized this early on and redefined the traditional crown gear technology with Eta Crown and Eta Crown Plus. The modern crown gear units in various sizes cover the reduction ratios in the single-stage range up to 10: 1, two-stage up to 113: 1 and three-stage up to 289: 1. In the one-stage range, they achieve efficiencies of over 90% and are more economical to produce than bevel gear units. Due to the principle, crown gear units also place less demands on the center distance setting than bevel gear units and achieve a reduction of 10: 1 from one stage.

User meeting mechatronic drive technology

The focus of the user meeting mechatronic drive technology is on the mechanical components of gears, clutches and brakes as well as their design, dimensioning and interaction in the overall mechatronic system.

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Angular gearbox: which design is the right one?

If you take a closer look at the structure of the various bevel gears, you quickly understand why crown gear units are a good choice for many applications.

Gears of bevel gearboxes have a conical shape. The gear function is only flawless if the center lines of the bevel gears intersect at exactly one point. Thermal expansion alone can therefore impair the function.

Worm gears are less sensitive, but the direction of the force flow is very unfavorable for them. The torque primarily causes a tensile or compressive load on the worm pinion. Since the pinion slides on the worm wheel, up to two-thirds of the input drive energy is converted into heat, depending on the reduction. The engine and transmission must therefore be dimensioned larger than is actually necessary in order to achieve the desired performance. In addition, the axial load on the screw must be absorbed by appropriately dimensioned axial bearings.

Book tip

The book Drive Design Practical Guide helps you select the essential components of electrical drive systems: motor, gearbox, actuator, power supply and their additional components. The calculation is also dealt with intensively.

Hardly any friction losses with the crown gear

It is different with the crown gearboxes Eta Crown and Eta Crown Plus from the EBM-Papst drive system: The involute drive pinion is cylindrical and the contact between the pinion and the driven gear is a rolling contact, there is hardly any friction loss. The efficiency is therefore in the range of 90% even at high reductions. The engine power is almost completely available for the drive task. 10% power loss compared to up to 75% with conventional worm wheel designs is an enormous saving potential even with small drives. Often, the drive motor can also be made smaller and space and costs can be saved.

Since the motor with the drive pinion and the output shaft are in one plane with the Eta Crown, the gearbox can also be installed mirror-inverted, which reduces storage and simplifies logistics.

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EBM Pope expands group management

Crown gear in use

There are many applications for which the crown gearboxes are recommended and in which they have proven themselves for many years. In addition to the high efficiency, typical reasons for their use are the high transferable torque and the lack of self-locking. In the case of barriers and access control systems , for example, the gears can be turned back manually in an emergency, even at high gear ratios, without the need for decoupling components to protect the drive from damage.

Thanks to the non-offset design, the motor-gear combination can also be easily integrated into the door profiles . There are no engine protrusions. This avoids recesses or additional spacer flanges to bridge distances. The symmetry in the gearbox design makes versions for left or right stop superfluous. The brake can be mounted directly on the drive shaft or, as usual, on the B-side of the motor, which simplifies the construction and makes the drive system more compact.

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Drives for medical devices

Other areas of application for the versatile right-angle gear units are, for example, pallet trucks or driverless transport systems (AGVs) . High transferable torques, durability and the compact dimensions speak for the use of a crown gear.

In medical technology , crown gear units impress with their reliability, smooth running and low heating.

Individual drive systems from the modular system

Eta Crown and Eta Crown Plus can be combined with all DC and EC motors as well as brakes and encoders from the EBM-Papst modular system. Individual complete drive solutions from a single source with coordinated components can be put together in the online portal.

Mechatronic drive technology

Optimal design of efficient drive system

On virtual paths against the corona crisis

In view of the latest developments relating to the corona virus, events are being canceled or postponed in a row. The future can belong to digital platforms that can compensate for this development. With the "Industrial Generation Network", the Vogel Communications Group presents a solution for professionals in the industry. As a digital supplement, the platform enables extensive networking: the focus is on digital encounters and establishing contacts, as well as product presentation and thematic exchange. Tools such as making appointments and video conferences enable professionals to network, make appointments and do research close to the respective branch. The platform thus replaces the currently severely restricted face-to-face communication, especially at trade fairs.

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* Friedrich Obermeyer works in the area of technology & methods for industrial drive technology at ebm-papst St. Georgen.