Spurred on by increasing demand from industry, the design of the gearing compo­nents of the crown gear­boxes and their manu­fac­turing tech­nology have been steadily improved. Combined with state-of-the-art EC motors, this creates compact and robust drive systems that effec­tively deliver power “round the corner” even in confined instal­la­tion condi­tions. They are typi­cally used in strap­ping machines as well as in auto­mated trans­port and shuttle systems, gate and cabinet drives, and in oper­ating tables as a sliding aid.

A new approach to crown gear­boxes

When it comes to angular gear­boxes, bevel gears or worm gears still spring to mind first for most people. However, there are always disad­van­tages when these are used, as worm gears have an offset between the input and output shaft as a matter of prin­ciple and work at compar­a­tively poor effi­ciency levels, so that the motor unit of the drive unit often has to be dimen­sioned larger.

Bevel gears are usually limited to a reduc­tion of max. 5:1 and are there­fore also usually not the ideal choice. Although their effi­ciency levels are very high, both the manu­fac­ture of the gearing compo­nents and assembly, espe­cially the align­ment of the gearing compo­nents rela­tive to one another, is compar­a­tively complex, some­thing which is, of course, reflected in the price. Anyone looking for an espe­cially econom­ical and effi­cient angular gearbox should there­fore turn to crown gear­head tech­nology.

High effi­ciency with large reduc­tion

If you take a closer look at the design of the various angular gear­boxes, you will under­stand quickly why crown gear­boxes are a good solu­tion for many appli­ca­tions. The gears of bevel gears have a conical shape. The gear func­tion is only perfect if the center lines of the bevel gears inter­sect precisely at one point. As a result, simply the thermal expan­sion during oper­a­tion alone can impair the func­tion.

Worm gears are less sensi­tive, but in their case the direc­tion of the force flow is very unfa­vor­able. The torque results primarily in a tensile or pres­sure load on the worm pinion. Since the pinion slides on the worm gear, up to 2/3 of the input drive energy is converted into heat, depending on the reduc­tion. The motor and the trans­mis­sion must there­fore be dimen­sioned larger than actu­ally neces­sary to achieve the desired power. In addi­tion, the axial load on the worm gear has to be absorbed by the corre­spond­ingly dimen­sioned axial bear­ings.

With the EtaCrown and EtaCrown­Plus crown gear­boxes from the ebm-papst modular drive system, this is different (Figure 1): The invo­lute drive pinion is cylin­drical and the contact between the pinion and the output gear is a roller contact; hardly any fric­tion losses occur. Effi­ciency is there­fore in the range of 90% even at high reduc­tions, making the motor power almost fully avail­able for the drive task. 10% power loss compared to up to 75% for conven­tional worm gear designs (depending on the reduc­tion selected) is an enor­mous poten­tial for savings even for small drives. In addi­tion, the drive motor can often be designed on a smaller scale, saving instal­la­tion space and costs.

Opti­mized gearing tech­nology and patented lubri­ca­tion

Crown gear­boxes of various sizes cover reduc­tions in the single-stage range up to 10:1, two-stage to 113:1 and three-stage to 289:1. The trans­mis­sions meet extremely strin­gent require­ments here. Together with the Insti­tute of Machine Elements (FZG) at Tech­nical Univer­sity of Munich, ebm-papst has conducted exten­sive research into all aspects of gearing tech­nology as part of a spon­sored project (Bavarian Research Foun­da­tion: AZ-1379-19; admin­is­trator: J.-F. Hochrein).

Figure 2: The enve­lope curve reflects the geom­etry of the crown gear flank. (Image | ebm-papst)

Figure 3: The linear load shows the force stan­dard­ized to millime­ters on the flank line of the crown gear tooth. (Image | ebm-papst)

Figure 4: The sliding speeds indi­cate how high the rolling speeds are at the crown gear flank. (Image| ebm-papst)

In this context, soft­ware has been devel­oped that can be used for the first time to real­is­ti­cally calcu­late para­me­ters impor­tant for design, such as geom­etry deter­mi­na­tions and gear contact analyses under load.

Enve­lope curves, for example, reflect the geom­etry of the crown gear flank and their boundary ranges (Figure 2) or the linear load (Figure 3) shows the force stan­dard­ized to millime­ters on the flank line of the crown gear tooth. The sliding speeds (Figure 4) indi­cate how high the rolling speeds are at the crown gear flank. The values are vali­dated on high-perfor­mance test stands and ulti­mately help to opti­mize produc­tion.

Improved lubri­ca­tion

Lubri­ca­tion has also been improved. In trans­mis­sions, there is usually the problem that the lubri­cant from the gearing areas of the trans­mis­sion gears is grad­u­ally displaced and accu­mu­lates in adja­cent areas. As a result, the gearing is not opti­mally lubri­cated over the service life, which can lead to exces­sive or prema­ture wear.

Figure 5: ebm-papst devel­oped a patented sepa­rating insert for the housing. (Image | ebm-papst)

Figure 6: The sepa­rating insert keeps the lubri­cant where it belongs, that is, on the gearing of the gears. (Image | ebm-papst)

This has now been prevented during the further devel­op­ment of the crown gear­boxes, as a patented sepa­rating insert in the housing keeps the lubri­cant where it belongs, namely at the gearing of the gears (Figures 5 and 6).

Drives for pack­aging tech­nology and intral­o­gis­tics

Typical appli­ca­tions for the versa­tile angular gear­boxes are in pack­aging tech­nology and intral­o­gis­tics, for example in auto­mated trans­port systems (AGV, auto­mated guided vehi­cles), mobile robots, and shut­tles (Figure 7). High trans­mit­table torques, dura­bility, and compact dimen­sions are points in favor of using a crown gearbox.

As the motor with drive pinion and the output axle are in one plane on the EtaCrown, the trans­mis­sion can also be installed mirror-inverted without any prob­lems, which reduces storage and simpli­fies logis­tics.

Crown gear­boxes are suit­able for many other appli­ca­tions. In addi­tion to the high effi­ciency levels, typical reasons for using them are the high trans­mit­table torque and the lack of self-locking.

Door and gate drives

In the case of barriers and access moni­toring systems, for example, in an emer­gency, the trans­mis­sions can be turned back manu­ally even in the event of a high reduc­tion without the need for compo­nents for decou­pling to protect the drive against damage. Due to the offset-free design, the motor-trans­mis­sion combi­na­tion can also be inte­grated easily into door profiles (Figure 8). There are no motor protru­sions. This avoids recesses or addi­tional spacers for bridging gaps. The symmetry in the trans­mis­sion design makes versions for left or right stops unnec­es­sary. The brake can be mounted directly on the drive shaft or, as usual, on the B side of the motor, simpli­fying the design and making the drive system more compact.

Appli­ca­tions in medical tech­nology

In medical tech­nology, crown gear­boxes excel in terms of their high reli­a­bility, smooth oper­a­tion, and low heating. They can be used as a sliding aid in oper­ating tables, meaning they can be moved without motor­ized assis­tance. EtaCrown and EtaCrown­Plus are part of the modular drive system from ebm-papst and can be combined with all DC and EC motors as well as brakes and encoders. Customized complete drive solu­tions from a single source with perfectly matched compo­nents can be combined easily in the online portal; thanks to defined preferred types, selected drive config­u­ra­tions are ready for ship­ment within 48 hours, which means that sampling, for example, can be done very quickly.