Planetary Gearset

Abstract

A method for designing a planetary gearset meeting one or more design targets is described. Initially, a size and ratio of the planetary gear set, and the number of planet gears for the planetary gearset is specified. All valid combinations of tooth numbers and planet numbers that satisfy one or more constraints are then calculated. From these, a starting combination is selected and a value for a design target for the gear set is calculated. One or more of the macro-geometry parameters are modified, and the macrogeometry parameters are chosen such that the positive effects of one macrogeometry parameter on the design target counteract any negative effects of another macrogeometry parameter. In this way, a design for planetary gearset meeting the one or more design targets is produced. Also disclosed is a method additionally calculating a sideband distribution resulting from the selected combination. The side band distribution is compared with a design target for sideband distribution and parameters are varied as necessary to achieve the required design.

1 . A method for designing a planetary gearset meeting one or more design targets, said method comprising the following steps:
 a. specifying a size and ratio of the planetary gear set;   b. calculating all valid combinations of tooth numbers and planet numbers that satisfy one or more constraints;   c. selecting a starting combination of tooth numbers, planet numbers, and planet phasing;   d. calculating a value for a design target for the gear set;   e. modifying one or more macro-geometry parameters; and   f. repeating steps c to e if a design target value is outside the design target range; characterised in that in the above step e), the macrogeometry parameters are chosen such that the positive effects of one macrogeometry parameter on the design target counteract any negative effects of another macrogeometry parameter and a design for planetary gearset meeting the one or more design targets is produced.   
     
     
         2 . The method of  claim 1 , in which the step of selecting a starting combination comprises selecting a starting combination having a small module and a large number of teeth. 
     
     
         3 . The method of  claim 1 , in which the design target is for bending strength, step f) comprising:
 i. calculating a bending strength of the gear teeth;   ii. modifying one or more macro-geometry parameters;   iii. comparing the bending strength with the design target for bending strength and repeating steps i and ii when the bending strength is outside the design target for bending strength.   
     
     
         4 . The method of  claim 1 , in which the macrogeometry parameter is module, step f) comprising:
 reducing power loss by reducing a contact length between two meshing teeth;   increasing bending strength according to one or more of the steps of:   i) increasing the pressure angle;   ii) increasing the helix angle;   iii) increasing the face width; or   iv) increasing the centre distance;   wherein a loss of bending strength resulting from the reduction of the contact length between two meshing teeth is counteracted.   
     
     
         5 . The method of  claim 1  additionally comprising the step of modifying one or more micro-geometry parameters 
     
     
         6 . A method of  claim 5 , in which one or more of the following micro-geometry parameters is modified:
 (i) profile crowning;   (ii) profile slope;   (iii) lead crowning;   (iv) lead slope;   (v) extent of tip relief;   (vi) form of tip relief (e.g. linear or parabolic);   (vii) extent of root relief; and   (viii) form of root relief (e.g. linear or parabolic).   
     
     
         7 . The method of  claim 5 , in which the micro-geometry parameters are optimised by using the Design of Experiments method, which can be automated in computer implementations to identify all permutations possible within user-specified tolerances, and determine the effects on design targets including efficiency, durability, or NVH in order for the user to select an optimum micro-geometry design based on a weighted combination of one or more design targets. 
     
     
         8 . The method of  claim 1  comprising the additional steps of:
 A. calculating a sideband distribution resulting from the selected combination; and 
 B. comparing the sideband distribution with a design target for sideband distribution and repeating steps c and A when the sideband distribution is outside the design target for sideband distribution. 
 
     
     
         9 . The method of  claim 8 , in which the step of calculating the sideband distribution includes using run out/assembly errors and transmission error. 
     
     
         10 . The method of  claim 9 , further comprising: calculating an extent to which high radiated noise is caused by an error. 
     
     
         11 . The method of  claim 8 , the step of calculating a sideband distribution comprising:
 calculating sideband distribution using mesh misalignment and transmission error using loaded tooth contact analysis.   
     
     
         12 . The method of  claim 8 , in which the planetary gearset is part of a machine, and the sideband distribution includes a frequency that is a known resonance in the machine. 
     
     
         13 . The method of  claim 11 , in which mesh misalignment includes one or more the following factors:
 i) non-linear bearing stiffness;   ii) shaft deflection;   iii) gear backlash;   iv) planet carrier stiffness; or   v) housing stiffness.   
     
     
         14 . The method of  claim 8 , additionally comprising the steps of:
 A. calculating the frequencies of other vibration modes in the planetary gearset;   B. comparing the spectrum of vibration modes to a design target for vibration; and   C. modifying any of planet phasing, planet number, tooth number when the vibration modes are outside the design target.   
     
     
         15 . The method of  claim 8 , in which a 6 degree-of-freedom dynamic model is used to characterise the system response to excitation from sidebands. 
     
     
         16 . The method of  claim 15 , in which the rigidity of the system can be optimised in conjunction with dynamic modelling of the system response. 
     
     
         17 . The method of  claim 1 , in which lubricant test data (for example, friction measurements from a mini traction machine) is integrated into an efficiency calculation using loaded tooth contact analysis. 
     
     
         18 . The method of  claim 1 , in which the step of specifying a size and ratio comprises specifying a packaging space and calculating size from a ratio, torque capacity, face width and a constant. 
     
     
         19 . A non-transitory computer readable storage medium encoded with instructions that, when executed by a processor, perform the steps of the method of  claim 1 . 
     
     
         20 . A machine including a planetary gearset designed according to the method of  claim 1 .