Planetary Reduction Gear Box
 
   
DESIGN AND WORKING PRINCIPLE
 
" SAVE POWER "
 

The heart of the planetary gearbox is the reduction group composed by the
the sun pinion (1) and three or more satellites (2) mounted on pins (4) which are supported by the satellite carrier (5).

The sun pinion transmits it’s motion to the satellites. The satellites then turn inside the ring gear (3) which is static. As consequence the satellite carrier rotates. The motion of the carrier can be transmitted to an output shaft or to another reduction group.
   
 
   
The reduction obtained is determined by the relation between the number of teeth on the sun pinion (Z1) and the number of teeth on the ring gear (Z2). The ratio can be calculated using the shown formula.  
   
THE ADVANTAGES  

The planetary gear box offers a set of advantages which makes it an interesting alternative to traditional gear types such as helical and parallel shafts gear boxes.

Especially in applications requiring:

  • high reduction ratios
  • high torque transmission
  • high radial loads on output shaft
    		•   
       
    In the following we shall explain why.  
       
    HIGH REDUCTION RATIOS  

    Given the same number of teeth Z1 and Z2 the planetary gear offers a higher ratio than the parallel shaft gear.    		  
       
    		 
       
    This makes it possible to obtain:

  • Higher ratios with a smaller number of stages
  • Stronger dimensions and thereby higher torque handling capacity
    		•   
       
    HIGH TORQUE TRANSMISSION  

    In a planetary gear the number of teeth in contact is higher than in a spur gear.
    Therefore, the planetary gear has a superior relation between torque handling capacity and dimensions.    		  
       
    		 
       
    HIGH RADIAL LOADS ON THE SHAFTS  

    In the planetary gear the internal forces are balanced, i.e. the resulting force is zero. The input and output shafts, therefore, are only transmitting torque.    		  
       
    		 
       
    In a parallel shaft gear, however, the internal forces are not balanced and the shafts must, therefore, support the internal loads.

    With the planetary gear it is, therefore, possible to have higher external radial loads on the shafts.    		  
       
    ADDITIONAL ADVANTAGES  

    Low noise level

    Despite the higher number of engaged teeth the noise level remains low as on traditional gear types because the smaller dimensions give lower peripheral velocity on the pitch diameter.
    Using input stages with grinded teeth on pinions and satellites combined with nitrided ring gears makes it possible to minimize the noise level of an in-line gearbox.    		  
       
    High efficiency

    Despite the higher number of engaged teeth the smaller tooth size makes it possible to obtain high efficiencies - typically 0.98 per gear stage.    		  
       
    Flexible ratio

    The ratio of a planetary stage can easily be modified by changing the sun gear and the reduction group.

    The ratio of a multistage gear can easily be adjusted by changing the ration of one or more stages.    		  
       
     

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