Methods and apparatus for reducing the sound level of a gearbox

Abstract

The present invention is directed to improved methods of reducing the sound level caused by meshing of gear teeth in a gear box, and in particular by reducing distortion caused by heat treatment as used in the manufacturing process of the gear teeth.

1 . A method of reducing the sound level caused by the meshing of gear teeth in a gear box, said method comprising reducing heat treatment distortion of the gear teeth.  
     
     
         2 . The method  claim 1  wherein heat treatment distortion of the gear teeth is reduced by use of hot rolled materials.  
     
     
         3 . The method of  claim 1  wherein heat treatment distortion of the gear teeth is reduced by use of cold rolled materials which have further been normalized and annealed.  
     
     
         4 . The method of  claim 2  further comprising removal of an outside layer of oxidation from said hot rolled steel.  
     
     
         5 . The method of  claim 4  wherein said outside layer of oxidation comprises approximately ¼ inch.  
     
     
         6 . The method of  claim 1 , further comprising carburizing said gears.  
     
     
         7 . The method of  claim 6  wherein carburizing comprises heating said gears to a pre-selected carburizing temperature in the presence of gaseous carbon, absorbing said gaseous carbon into the surface of said gears, thereafter quenching said gears, and subsequently tempering said gears.  
     
     
         8 . The method of  claim 7  wherein said gears include hubs, and wherein the hubs of said gears are increased in thickness to act more uniformly during quenching.  
     
     
         9 . The method of  claim 7  comprising reducing residual stress prior to heat treating said gears.  
     
     
         10 . The method of  claim 9  wherein said gears are formed by machining tools and wherein residual stress is reduced by maintaining the sharpness of said machining tools during gear machining.  
     
     
         11 . The method of  claim 9  wherein said gears are normalized to reduce residual distortion prior to machining.  
     
     
         12 . The method of  claim 7  wherein said gears are heated to said pre-selected carburizing temperature, cooled to room temperature,  
     
     
         13 . The method of  claim 6  further comprising establishing standards for the hardness of and case depth of said carborized gears.  
     
     
         14 . The method of  claim 13  further comprising testing said hardness and case depth thereof after carburizing said gears.  
     
     
         15 . The method of  claim 7  wherein said heating during carburizing of said gears is carried out at approximately 1500°-1900° F.  
     
     
         16 . The method of  claim 7  wherein said tempering is carried out at approximately 375°-600° F.  
     
     
         17 . The method of  claim 16  wherein said gears are tempered at temperatures below approximately 500° F.  
     
     
         18 . The method of  claim 1  wherein the sound level is reduced to less than approximately 77 dB.  
     
     
         19 . The method of  claim 1  wherein the sound level is reduced to less than approximately 83 dB.  
     
     
         20 . The method of  claim 1 , further comprising the substantial reduction or elimination of gear whine and wherein the gears of said gearbox are disposed in profile mismatch array between contacting gear teeth to reduce gear whine.  
     
     
         21 . The method of  claim 20  wherein said gear teeth include a tooth root, a tooth bottom, and a tooth flank at the top of said gear tooth, and separation is maintained between said tooth root and said tooth flank to reduce gear whine.  
     
     
         22 . The method of  claim 20  wherein said gear whine is substantially eliminated.