Crown gear­boxes were already used in tech­nical systems a century ago and can still be seen today in historic mills. Over the course of time, they were displaced by bevel gears because these were easier to calcu­late; the crown gear disap­peared from the market. However, this changed when the focus shifted to energy-effi­cient drive tech­nology in industry and to smaller drives. After all, the right combi­na­tion of effi­cient motors, gear­boxes and control systems enables high energy savings in the power range below 250 W.

The effi­ciency is also in the range of 90% at high reduc­tions.

As decen­tral­ized drive tech­nology has become more impor­tant in machine and plant engi­neering due to its flex­i­bility, there is an increasing number of such drives. Trans­mis­sions that operate at the highest possible effi­ciency are there­fore in demand, and this is where crown gearbox tech­nology can score points. The gearbox specialist Zeit­lauf, which is now part of ebm-papst, recog­nized this early on and re-defined tradi­tional crown gear­head tech­nology with EtaCrown and EtaCrown­Plus (Fig. 1).

Figure 1: The EtaCrown crown gear­boxes (here as a motor-trans­mis­sion combi­na­tion) cover the reduc­tion range from single-stage to 10:1, two-stage to 113:1 and three-stage to 289:1 in various sizes, achieving effi­ciency levels of more than 90%. (Photo | ebm-papst)

State-of-the-art crown gear­boxes of various sizes cover the reduc­tions in the single-stage range up to 10:1, two-stage to 113:1 and three-stage to 289:1. In the single-stage range, they achieve effi­ciency levels of more than 90% and can be manu­fac­tured more econom­i­cally than bevel gears. Due to their prin­ciple, crown gear­boxes also place fewer demands on the center distance adjust­ment than bevel gears and even achieve a reduc­tion ratio of 10:1 from a single stage (bevel gear: 5:1).

Great effi­ciency with high reduc­tion

If you take a closer look at the design of the various crown gear­boxes, you will under­stand quickly why crown gear­boxes are a good choice for many appli­ca­tions: Gears of bevel gears have a conical shape. The gear func­tion is only perfect if the center lines of the bevel gears cut at exactly one point. As a result, even thermal expan­sion can impair the func­tion. Worm gears are less sensi­tive, but with them 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, depending on the reduc­tion, up to 2/3 of the input drive energy is converted into heat. 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.

Figure 2: In crown gear­boxes, the invo­lute drive pinion builds in cylin­drical form and the contact between the pinion and the output gear is a roller contact; hardly any fric­tion losses occur. (Photo | ebm-papst)

With the modern EtaCrown and EtaCrown­Plus crown gear­boxes from the ebm-papst modular drive system, this is different (Fig. 2): The invo­lute drive pinion builds in cylin­drical form and the contact between the pinion and the output gear is a roller contact; hardly any fric­tion losses occur. The effi­ciency is there­fore also in the range of 90% at high reduc­tions. The motor power is thus almost fully avail­able for the drive task. 10% power loss compared to up to 75% for conven­tional worm gear designs is an enor­mous poten­tial for savings even in small drives. It is often also possible to dimen­sion the drive motor smaller and save space and costs. As the motor with drive pinion and the output axle are in one plane on the EtaCrown, the trans­mis­sion can also be installed easily mirrored, which reduces storage and simpli­fies logis­tics.

Advan­tages in the appli­ca­tion

Figure 3: The motor-crown gearbox combi­na­tion can be inte­grated into the profiles due to the offset-free design. There are no motor protru­sions, which prevents recesses or addi­tional spacers for bypassing inter­vals. (Photo | ebm-papst)

There are many appli­ca­tions for which crown gear­boxes are recom­mended and in which they have proven effec­tive for many years. In addi­tion to the high effi­ciency levels, typical reasons for using them are the high trans­mit­table torque and the lack of self-locking. In the case of barriers and access moni­toring systems, for example, 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 (Fig. 3). There are no motor protru­sions. This avoids recesses or addi­tional spacers for bypassing distances. The symmetry in the gear 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.

Crown gear­boxes impress with their great reli­a­bility, smooth oper­a­tion and low heating.

Other appli­ca­tions for the versa­tile crown gear­boxes include lift trucks and auto­mated guided vehi­cles (Fig. 4). High trans­mit­table torques, dura­bility and compact dimen­sions speak for the use of a crown gearbox. In medical tech­nology, crown gear­boxes impress with their great reli­a­bility, smooth oper­a­tion and low heating.

Figure 4: Crown gear­boxes are suit­able for use in guided vehicle systems: The effi­cient trans­mis­sion ensures safe and flex­ible move­ment. (Photo | ebm-papst)

EtaCrown and EtaCrown­Plus are part of the ebm-papst modular system 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.